Alocasia reginae growing in Gunung Mulu National Park in the Malaysian State of Sarawak. Photograph: Peter Boyce. — *Alocasia reginae* growing in Gunung Mulu National Park in the Malaysian State of Sarawak. Photograph: Peter Boyce.

Transcript

Episode 193

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Jane: Hello and welcome to On The Ledge podcast with your host, Jane Perrone - planty to the core! In this week's show I am joined by Peter Boyce, Aroid researcher and the honorary president of the newly formed European Aroid Society. We talk about the new society, developments in the world of Aroids, both horticultural and scientific, why we all get very confused about Aroid leaf shape and a fascinating, vanilla-scented Aroid that you've probably never heard of! Plus, I answer a question about potting plants with no drainage hole. Oh, daring!

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Jane: Hello and thank you for joining me for the final episode before my summer break. If you are listening to the show at some point in the future, then hopefully you can just skip on to the next episode, but if you are here with me in July 2021, then the next episode will be out on 10th September. If this is sending you into paroxysms of fear then I have a few suggestions! I have done 190-odd episodes of the show, so maybe you've missed an episode, or you want to go back and listen again. There's a thematic list of episodes which I will share in the show notes. At the bottom of that page there's also a list of other podcasts I've appeared on and there's at least twelve or fifteen of those, so there's plenty of material to be going on with. I'll be posting some links on social media over the coming weeks, of other talks and things that you might be interested in having a look at, to fill that OTL-shaped hole in your life!

Thank you to everybody who responded to last week's episode about mental health with Amy March from PerkyPlants; a really great response from many people who found the episode helpful, found that themes resonated in their own lives and were nodding along as we talked about the challenges of plant overwhelm, depression and more. I had a message from someone we'll call M, who felt like that episode was talking directly to them and they write, "I never realised that situation could be plausible or even understandable to someone." M's somebody who suffers from chronic depression and anxiety and finds it difficult to function in life and M writes, "Sometimes my passion for houseplants feels like a shallow hyper-fixation. After all, how can someone spend hours caring for their plants but not be able to brush their hair? I must be faking, or lazy, or the depression is just all in my imagination, even though I've been formally diagnosed for years now. These thoughts come during times when I'm feeling resentful towards myself and frustrated at how my life is going, but I'm beyond grateful that humanity has come up with the activity of plant cultivation because, otherwise, I would feel utterly lost." M goes on to describe a situation where a panic attack managed to be stopped in its tracks by plants: "I just wanted to share this with you in case it's a useful technique for anybody. There's a technique for dealing with anxiety where you focus on your surroundings and describe them to yourself. It's fairly well established and you may have heard about it." M decided to bring their plants into this and M writes, "I was, of course, surrounded by my plants and I went 'round to each one saying out loud to myself everything I knew about the species but also, more importantly, the story behind that individual plant since it came into my care. I've never calmed down so fast before and I hope other plant owners who struggle like I do can find some benefit in this technique." So there you go, that's a great one to try for anxiety and thank you to M for getting in touch and telling me about that. I know it's sometimes not easy to share but this is how we help each other out.

Lena got in touch about lots of different things, including her desire for everyone to join plant societies, which I think I would definitely concur with. Lena's been collecting orchids for about fifteen years and found that their collection fluctuated depending on how they felt. I think we can probably all sympathise with that. Lena writes, "Combined with social media, glam post pressure, addictive personality and depression has left me feeling disgusted with myself at points where I just kept pressing 'Buy' and saying 'This is the last one', even though I knew this will have to come out of the overdraft or a credit card. Thanks for bringing attention to this issue." This is a theme that really resonates with lots of us, doesn't it? So let's keep talking about it, discussing it, bringing it to the fore and normalising checking on each other in a caring way, recognising both the pluses and the less positive bits of the houseplant hobby.

Let's crack on with this week's interview which comes from Peter Boyce. Peter is a plant taxonomist and biologist and he's based in Sarawak, the Malaysian state that takes up the north west corner of Borneo, and in partnership with his wife, Wong Sin Yeng, he researches Aroids. He's also taken up the role of honorary president of the newly formed European Aroid Society. So in this interview we go from the basics - What's an Aroid? - we find out a bit more about the EAS and its aims, cover some top tips for helping climbing Aroids to secure themselves and a lot more. Do check out the show notes for this one: loads of great images and information to go with the interview as you listen.

Peter: I'm Peter Boyce, I'm a plant taxonomist and biologist working in Southeast Asia, based in Sarawak, which is on the north west corner of the island of Borneo and it's one of two bits of Malaysia that make up the island of Borneo, together with Brunei and the bulk of the island is Indonesia and Borneo, Kalimantan. I run a tissue culture lab, doing plantation crops, but I'm also a researcher for tropical Aroids, tropical araceae, so the syngonium philodendron family.

Jane: It's great to have you on the show! Can you just fill us in on what classifies a plant as an Aroid?

Peter: From a perspective of people's knowledge of houseplants, it's things like Peace Lilies, epiphyllum, anthuriums, the so-called Tail Flowers, Philodendrons, Monsteras and so on. From a biological standpoint, what defines the family is having a finger-like structure on which the flowers are arranged surrounded by a colour, usually colourful, leaf-like structure, which is termed a spade. It's like a bract surrounding this finger of flowers. They're the two defining characters that are visible easily. The third character, from the biological point, is that individual flowers on this finger-like structure don't have a little bract underneath them. Now, that sounds incredibly trivial, but if you start pulling apart flowers of things like Buddleia or Stephanotis, which had their flowers in clusters, every flower's got a little structure at the base, like a tiny green leaf, which is called a bract, or a bractiol, to be really accurate. Aroids lack those and that's unique in the plant kingdom.

Jane: There is a certain section of these Aroids that have become of huge interest to houseplant collectors of late. I think those of us with longer memories will probably realise this isn't the first time that this has happened, but what is it about Aroids that you think makes them, or this particular segment of Aroids, that makes them good houseplants and the subject of such feverish excitement?

Peter: The feverish excitement, I think, is the fact that one of the most popular groups now are things like Philodendrons and Monstera. With Monstera, the craze at the moment is how many holes has the leaf got? You end up with these remarkable, almost Belgian lace leaves, which I think many people find very beguiling. With Philodendron, the new leaf colour is very different to the mature leaves, so as the plant grows, you've got this constant flash of bright pink, or bright green, or yellow-green leaves, which then age to variously variegated leaves, so that's where a lot of the passion is from. What makes them good houseplants is a slightly more awkward, not an awkward -- it's the wrong word - slightly more problematic. Monstera, the Swiss Cheese Plant, is a monumental climber in the wild. It would climb to 20 metres up a tropical tree which, if you think about windowsills in European cities, is really not immediately an obvious choice but because they perforate their leaves early on and they are kept manageable by trimming them back, people think they are a manageable houseplant. Indeed they are manageable houseplants, but if you look at them from the perspective of what they do in the forest, they are the most unlikely houseplants you could imagine, with these colossal climates and yet, because they are amenable to being chopped back and kept on windowsills and, by and large, are pretty tough things, the ones that are most popular, they are, in many ways, the ideal houseplant. Dieffenbachia, the Dumb Cane, has been a popular houseplant for 50 years; a plant in the wild that grows in tropical swampy areas, so there's a paradox. On the one hand, if you look at them from a cold perspective of what they do in the wild, they're the most unlikely plants for houses and yet because they're easy-growing and they're attractive and they have variegated leaves and perforated leaves, partly-coloured growths, they become enormously popular, which is quite exciting actually.

Jane: I wondered about that, how you feel about this huge surge of interest in Aroids? I mean, it's exciting. Is it also worrying, in that it's leading to plants being taken from the wild, particularly where you are?

Peter: Well, there's another interesting paradox in there, actually. Although there's a huge amount of noise, justifiably, about the removal of industrial quantities of plants from the wild, the truth of the matter is the large percentage of the greatest, most popular groups, are already in cultivation. It's just that people have cottoned on to the idea that variegated forms of Philodendron billietiae or preposterously perforated leaf-form of the Monstera adansonii or Monstera obliqua are marketable. A lot of these plants have been in cultivation, tucked away in the backs of nurseries, for decades, and yet suddenly this balloon has come up, whereby they're suddenly popular and the more outlandish the colour form, or the more outlandish the amount of holes in the leaves, the more dollars the plants attract. So that part of it doesn't worry me. I mean I think some of the prices being paid are frankly ridiculous, but that's market forces. With regard to stripping out from the wild to supply the international market, with probably the exception of Alocasia, that isn't such a big issue as everyone seems to think. The one genus that concerns me, especially with this part of the world, is Alocasia. That's where my concerns are, partly because a lot of them occur in very small areas in the wild and partly because some of the removal rates are really, very disturbingly almost on an industrial scale. So I'm between two poles on this. A lot of the big profit-generating plants have been in cultivation many, many years. It's just, suddenly, people have woken up: "Oh, that's actually quite a special plant!"

Jane: Can we talk a little bit about the Rhaphidophora genus, the one species that seems to have broken through in terms of the global houseplant market is what's called Tetrosperma and I say that because I've seen various discussions about this species and whether it is this species and variations. Can you shed any light on that as a taxonomist?

Peter: I've given up commenting on these discussions because, basically, Rhaphidophora tetrasperma is an incredibly well-defined species. It doesn't grow in Borneo. It's a peninsular Malaysia species and it gets into the far south of Thailand, below the Isthmus of Kra and in the wild it's usually, but not always, associated with cast limestone. There are populations that aren't on cast. The big problem is that most people growing climbing Aroids make two big mistakes: one is they don't give them a suitable climbing surface, they try to pin them to bamboo sticks with twist ties and things and the other thing they don't give them is enough light. Now, Rhaphidophora in the wild go through various growth phases and there's a terrestrial phase where the plant in the forest is looking for climbing surfaces. So I won't get into all the technical words for this, but they seek dark areas, these long whippy shoots, in order to begin to climb, to go up into the light, to go up into the canopy, to flower, onto the rock surface in the case of Tetrasperma. The thing is, the leaves on these long, whippy shoots are very, very different in appearance to the leaves that the same shoots begin to produce once they begin to climb. Those same shoots will produce yet different leaves again once the shoot apex gets into an area with good light. So, a lot of what you see on the web, where people say "This is Tetrasperma but it hasn't got holes", or "This is a Tetrasperma but it's only got divisions and no perforations" and then I'll show Tetrasperma with holes in the leaves and say, "Well, this isn't Tetrasperma. This is pertusa," are all Tetrasperma. Then there's this thing about how the plants are modified because of tissue culture. This is frankly, actually, quite nonsense! All that's happening is that the various growers who are posting their individual plants, are not comparing the conditions they grow their plant in with the conditions another grower who posts his or her plants are growing under. We have five kinds of Tetrasperma on the nursery: two from Kelantan, one from central Malaysia, from Pahang and one from southern Thailand. Allowing for a little bit of variation, they're all very stable. Once the leaves get into the light, they get much bigger and they start to produce perforations. Until that point, the leaves remain rather small and only have sort of splits in the sides, but no holes and no sort of clinging tips of the individual leaf lobes. Further confusion, is people who are growing Rhaphidophora**pertusa, which is a species from India and Sri Lanka, and are mixing the two up.

Jane: You mentioned there about the incorrect ways of trying to support climbing Aroids.

Peter: Sub-optimal, shall we say.

Jane: Sub-optimal, okay, that's a good word! What's the optimal way if you are growing them in a houseplant situation? What's best practice?

Peter: Totems are okay, but this business about keeping the totem wet is a bit pointless. As long as the plant is misted semi-regularly, the best thing to do is, if it's not too big, haul it into the bathroom and run the shower on it for a few moments just to dampen the stems. The roots of the climbing stems will very happily adhere to a dry totem. Now the idea that the totem's got to be wet to enable the roots to stick is just fallacious. It's just not true. Even better, although this starts to get a bit awkward if you're dealing with plants on windowsills, is a section of cork wood. The orchid people grow on slabs of cork. Getting some slender strips of cork, maybe attach them to a lightweight plastic drainage pipe, a one half inch plastic pipe, because cork, because of all the fissures and so on, is ideal surface for climbing Aroids. Cork is sustainably managed as well. It's not cheap, but moss on totems is not sustainably managed, by and large. So, a strip of cork or, although it's not very attractive if you're looking at plants indoors, but a baton of rough wood. This is what the Victorians used. The Victorians used to grow on batons of rough wood. For climbing orchids too, that works very well. A wigwam of bamboo sticks and lots of twisted ties, the plant will survive, it won't prosper.

Jane: That's fascinating and I'm loving the idea of the piece of rough wood. I guess, hopefully, if your Aroid is growing well, it will be colonising the wood and you might not end up... you're going to be looking at the leaves rather than looking at the piece of wood?

Peter: Yes and it needs to be a reasonable length. A six inch piece isn't going to work. It'll work for maybe the first few weeks. It needs to be a decent... I'm not suggesting some huge sort of great big pole, but if you could manage three foot, a metre, then you could get some pretty decent growth and that would look very nice.

Jane: Well that is really good advice. It is wonderful to have your input on that because I know lots of listeners ask questions about moss poles and all these different issues, so that's really useful. Now the EAS, the European Aroid Society, this newly-formed society for Aroid fans. What do you think the society is going to bring to the Aroid community? Presumably there's been a great demand in Europe for some kind of community set up around this subject?

Peter: Yes, I mean there's always been a core of growers in Europe and many of which will be involved with the society directly already. People like David Scherberich in Lyon, and Enimie and Nils Weessies in the Netherlands, Enimie in Belgium and then Geneviève Ferry in Nantes and they've always been there. There's always been a, sort of, core of keen - they're all professional growers or very keen amateurs in the case of Enimie and Nils - and then there's always been a core of keen growers. What's happened is, and it's tempting to link it to this current business with Covid, but there has definitely been a huge upsurge inAroid interests which does seem to be linked to a longer period where people have been confined to home. Now, I'm not correlating those two at all, but yes it does look pretty convincing. So there's a very, very active Aroid set in Europe now, and a few thousands of people, and the society partly came about to enable them to communicate, directly and indirectly: directly through the society website and the society's Facebook and a little bit less so for Instagram and Twitter, and indirectly through the society newsletter, which the first issue has just been published. Now, the newsletter is unavowedly non-scientific by definition. That's the plan at the moment. The society, at some point, might start producing a scientific journal but, at the moment, it's all about allowing keen growers - amateur growers, professional growers, keen hobbyists, houseplant enthusiasts - to communicate about the plants they like and there was a lack of that facility in Europe and no doubt about it.

Jane: It's going to be a really great opportunity for people to get something in the way of expert advice because I think that's one of the problems: in the world of social media, there's a lot of people out there talking about Aroids, not all with enough knowledge to be speaking with authority, if I could say that?

Peter: Yes, I think that's incredibly polite actually. There's a lot of nonsense spoken, actually, and some of it is quite misleading. Then new growers, they call themselves newbies, get very disappointed because they spend quite a bit of money on a plant and they're told something completely unreliable, or misinformation, which a lot of people repeat. It's like the ice cube and orchids business. Is that growing an orchid? It's not quite that bad but it's in that league. So, no, great they've got somewhere to key into now, where they know there's someone like David or Nils who are really good, competent growers and who can say, "Hey, well, no! I wouldn't do it that way! Maybe try this". So yes, it's terrific.

Jane: I guess, also, the wonderful thing about Aroids, the ones that are grown as houseplants, they are often very forgiving?

Peter: Absolutely, especially Aglaonemas, Dieffenbachias, certainly the Philodendron hybrids. They're extraordinarily forgiving plants, actually. Far more so than, say, cactus or succulents or, dare I say, windowsill orchids. Yes, indeed.

We'll be back with more from Peter shortly, after this break.

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Jane: What is coming along in the world of Aroids that perhaps my listeners won't have come across yet but is on the way? What's the hot topics that, as Aroid experts, you and the board members are talking about?

Peter: Horticulturally, or scientifically?

Jane: Well, let's start with horticulturally.

Peter: Right, well, I think one of the most exciting things is the extraordinary diversity of Aroid species that are coming into cultivation. Now, this may start to edge into some slightly less wonderful items regarding collecting plants in the wild but, nevertheless, there's no doubt now that there is probably more diversity of Aroid species available now than any time in the past, ever, including the big Edwardian/Victorian phase for horticultural plants in the UK and in Western Europe. So the diversity available is astonishing and it's increasing. The number of Anthuriums in cultivation now is easily a few hundred, of which, probably a good two-thirds are readily available in terms of finding them from semi-specialist growers rather than your local garden centre. What's interesting is a lot of these new, rare things that appear, initially in specialist grower nurseries, they catch the eye of large wholesale garden centre suppliers and then they start to get involved with mass propagation, mass production, and suddenly, a thing that's incredibly rare and difficult to find, now, three or four years down the line it's, well, not quite supermarket, but decent garden centres are often on sale. That's very exciting. So the prices start to drop and then people think, "Oh, I'll try that because it's three or four quid" rather than, "Oh, that's £150. I can't afford that!". So that filter through is very exciting, the fact that this huge diversity that's available now in specialist collections filters through into the more general. This has happened with cactus in the past as well. Ultra-rare cacti get propagated and suddenly a thing that was impossible to find for sale 10 years ago, you can pick it up in a garden centre, not necessarily very cheaply but at least availability, so that's, I think, the most exciting thing of all. The society will be very much part of that because of the availability of information to say to people, "Well, this is something that's worth buying if you see it for sale for a few euro, or a few pounds. Pick it up because this is worth having!"

Jane: Let's move on to scientifically. I know there's loads of work going on with various genera in terms of taxonomy. What's your potted summary on that?

Peter: How many hours have I got? Well, there's one... this probably will be of absolutely no interest whatsoever to 99% of your listeners, and that's not meant to sound patronising, but there's a new phylogeny coming out, there's a new taxonomic framework coming out, I can't talk about it in too much detail because it's not in the public domain. A number of botanic gardens and specialist researchers and industries growers and botanic gardens have been involved, in the last few years, with supplying leaf material for molecular analysis to create a new kind of framework for relationships, so we understand more and more and more about how things are related. Now, this might sound as dry as dust, but from the point of view of the society, although it is very much, at the moment, a growers' society, which is what it should be, the fact that we can plug into this information because some of the board members have been very actively involved with this big project is rather exciting. It puts the society's feet in two places; it puts the society's feet firmly on the side of the growers and hobbyists, ornamental, commercial nurseries, people who are new to growing Aroids, but it also gives a link through for them, for those who are interested, into what we understand about how these things are related and that's very exciting that the society is involved with that. Although the society has come in after that project started, there are members of the board who have been very actively involved, so that's very nice. Also, we're beginning to get a lot more understanding about pollination biology. Now that, again, may not sound terribly interesting, but it starts to open up business for, "Well, we know that these two things are very closely related and we know their pollination is similar. Let's try some hybrids". Now, I'm not a big fan of hybrids but many, many, many people are. An example would be Colocasia t**aro and Alocasia. Now, they don't hybridise easily, but there's now an intermediate genus, like Colocasia, which hybridises with both. So then you start getting involved with, "Well, maybe we can get the best characteristics of two or three things that are hard to grow, into a plant that's easy to grow". So, yes, that's the scientific side. It fits into the horticultural side quite neatly, even though some of the science might seem terribly esoteric and ivory tower.

Jane: I think there is a lot of discussion about some of, can I say, more blunt issues, of taxonomy of Aroids on social media and, again, as we talked about with Rhaphidophora, oftentimes it's not entirely accurate. I see so many discussions about "Is this Monstera deliciosa large-form Borsigiana?" and all these different things. So I think, in a way, there is a segment of the hobby growers who will be delighted to have some more clarity about taxonomy.

Peter: Absolutely. The nice thing with Monstera is that there's a very young, very capable and incredibly enthusiastic Costa Rican student about to begin a PhD on Monstera, who's been working on a Master's degree and that is rather exciting: the fact that there's this chap who's been working on Monstera, and there's a big paper coming out soon, which will clarify some of these names and some of the names that are being used are incorrectly applied to things that are actually undescribed, which is rather nice. So people will discover the thing they've got as Borsigiana is, in fact, not Borsigianaat all! It's actually an undescribed species, to take an example. So, yes, there is interest out there.

Jane: Yes, that's exciting.

Peter: Yes, I think so.

Jane: I think that's perhaps part of the appeal of Aroids, is that you've got things that are variable and change over time. I think it's fascinating the way that the Aroid leaves vary, from the juvenile form to the adult form and in between.

Peter: We still don't understand why that happens.

Jane: I think this is one of those things that does happen in nature. I'm thinking of Ivy, Hedera helix here in the UK, which, when it gets to the top of a fence or a tree, the arborescent form of the leaves is very, very different from the juvenile form.

Peter: That's right.

Jane: I think we notice it so much more in our houseplants but there are plants which people don't even recognise when they get to the adult form. I'm thinking of Devil's Ivy, of course, which is the classic one which you very rarely see in the west.

Peter: You can never get it big enough.

Jane: The only place I've ever seen it is at RHS Wisley, actually, where they have got a really big one going up a pillar.

Peter: It grows on lamp posts here. It's somewhat weedy in Sarawak, it grows on lamp posts and on the top of the lamp posts, it'll indeed form these enormous split leaves, that's right, but in a pot you'll be hard-pressed to get it big enough.

Jane: Indeed and I just want to go back to the very beginning of this interview, when you were talking about a Monstera deliciosa growing up trees, because I've never seen one growing in that natural situation. I've seen big ones in botanical gardens and things, but I'd love to know what it actually looks like and what's going on when it does its wild thing and grows up a tree. As you've described it, presumably the young shoots are moving towards the dark to get to the tree, or whatever it's going to grow up, on the ground. Anyone who's growing this plant as a houseplant will know about the spaghetti monster of aerial roots that develops.

Peter: Most climbing Aroids, and Monstera deliciosa is certainly in this category, produce two sorts of roots and they'll produce a very short, or comparatively short, clasping root which will hang on to the climbing surface and then, as this plant begins to grow higher, they'll start to produce much longer roots. Now, some of those roots may well indeed travel down the tree trunks into the ground and others will hang free in the air and penetrate the ground. These much longer, usually much more robust roots, they are the roots that bring liquids and nutrients to the plant, so they don't have a clasping role. Obviously those that grow on the tree trunk will hold the thing in place to a certain extent. The job of holding the climbing stem to the tree trunk is the job of the clasping roots and they're comparatively short and stubby. So the long curtains of roots hanging down they have a different role and it's important if you're growing these things in pots to make sure those long hanging roots go into the pot because they will then ramify in the pot and the plant will have a lot more availability of nutrients and liquid than if you just let them hang on the bathroom floor.

Jane: Yes, that's really interesting. I've seen, again, a few Instagram hacks where people are putting them in a glass of water but I imagine it's much better for them to be going into the soil in the pot?

Peter: Yes, you can put them in a glass of water but, yes, they're better off growing into a suitable growing medium, indeed.

Jane: Some people recommend cutting them off. If you cut them off, aren't they just going to regrow?

Peter: Yes, they'll just branch. If you cut them off you'll get three roots where there was one. The root is, basically, a very tough structure so if it gets damaged, and they get damaged in the wild pretty regularly, they just branch. So don't cut them off! Put them into the pot.

Jane: Yes, I guess that's the idea. It does give them a different look but I think it's, as you say, people have got a slightly wrong image of what these plants actually look like.

Peter: We call them feeding roots, incidentally. The critical thing is that they are the plant's primary source of liquid and nutrients. The actual stem in the pot, by nature, will not last forever. If you go into the forest where there are big populations of big climbers, it's very hard to see where the plant originally started growing because the stem that originally came out of the ground was long ago deceased. So the plant has re-attached itself to the ground through these long roots and through long whippy stems that have hung down and re-rooted and re-climbed. So if you constantly don't allow those long roots in cultivation to go into a suitable soil the base of your plant will eventually, once it gets big enough, will wither and die because that's what they do they, basically, grow up and the older bits die away. Once that happens, if the plant hasn't got enough roots in the pot, then you're going to lose it, or at least struggle to keep it happy.

Jane: Let's talk a little bit about Scindapsus, if we can? I'm sorry, I'm going slightly off list here, but you're saying lots of interesting things that I want to talk to you about, which is usually what happens in one of my interviews!

Peter: No sweat - don't worry!

Jane: Let's talk a little bit about Scindapsus because this is a really fascinating genus. Tell me about Scindapsus. I don't have any specific questions. I'm just fascinated to know what you know!

Peter: The big thing online at the moment are all these multitudinous colour forms of Scindapsus pictus, Platinum and Jade. There's thousands of these named ones. The thing to remember with all of these plants that are being bandied around with these fancy names on, the plants with the colour patterning are all the juveniles. Once Scindapsus pictus in any manifestation begins to climb and produces adult leaves, or semi-adult leaves, the patterning will disappear. Quite a few times on Facebook, in particular one plant that we know quite well in an area of forest in central Sarawak, where, on the floor of the forest, is covered in a really nice form of pictus, a lovely sort of scintillating, spattered grey and green leaves, but all the adult stages, climbing up the trees nearby, are a plain dull green and, basically, that's the same plant. So a tip for people growing Scindapsus pictus, one is, it's all pictus. If you want to call it Jade and Platinum, that's fine if that helps you identify that colour form from another colour form. It's all pictus. The second thing is you've got to keep it cut. If it starts to produce adult growth it will lose its colouration. Pictus is very widespread in the wild, from southern Thailand, right through to Sumatra, the whole of the peninsula of Malaysia, whole of Borneo, Java, out into the Philippines, so it's a very widespread species and, as you might expect, it's highly variable. The colour forms, some of them are spectacular, but it's a transient thing. If you let the plants begin to become adult, you'll lose the colourfulness. The colour will disappear from the leaves.

Jane: Do we know what benefit that gives the plant, being variegated at that juvenile stage?

Peter: It's probably a camouflage thing. There are some studies done in the US, not entirely convincing data but sort of pointing in the right direction, not for Scindapsus, it isn't, but for other groups of plants. It's probably a camouflage thing. The leaf colour breaks the leaf outline up. So herbivorous creatures see the leaf as pre-damaged and there's some reasonable evidence that this patterning helps the leaves avoid being eaten. The scintillating ones, the one where there's a fractionating of light, it might be a way of getting more light into the chloroplast, or the leaf - a bit like Begonias often have red backs of the leaf which bounces green light back into the leaf. That's all a bit sort of speculative. It is interesting that almost none of the climbing Aroids with variegated juvenile stages retain that colour into the adult phase. Monstera dubia doesn't, Scindapsus pictus doesn't, Scindapsus treubii doesn't, Epipremnum amplissimum doesn't. So it's clearly an advantage to the juvenile phase, to have a patterned leaf and the anti-herbivorous thing is semi-compelling.

Jane: Yes, it does kind of make sense I guess. Once they're up in a tree, there's going to be less herbivores around trying to chew on them.

Peter: Exactly. The problem with that story with Rhaphidophora and Scindapsus, of course, is that the leaves are incredibly unpleasant to eat. They're full of nasty chemicals and they're full of these calcium oxalate crystals. You chew on a leaf of Monstera and it's something you'll regret! It's like eating nettles, but not all things are affected by nettle leaves so, perhaps, it's the best fit we've got at the moment.

Jane: I guess that's what's fascinating is there's always something new to learn, isn't there? We're still learning. It's really interesting to hear that and it reminds me of all the fuss about different forms of Philodendron hederaceum, which is the same kind of scenario.

Peter: Yes, indeed. Also a widespread species.

Jane: Yes, that seems to be endlessly variable in terms of its appearance, in the juvenile form anyway. I wonder is it the same with the adult form?

Peter: Yes, they're all green. We have Rain Tree in the nursery. These are big legume trees, colossal legume trees, actually, covered in Philodendron micans, which is one with this sort of coppery juvenile phase, the juvenile leaves are this wonderful sort of burnished, scintillating copper. The adult leaves are cordate and leathery and medium green... another green Philodendron.

Jane: That's so interesting.

Peter: The juveniles are very pretty.

Jane: I guess, in a way, this is part of the key to why they're attractive as houseplants, in that, if it was the other way round, possibly they wouldn't be?

Peter: Absolutely. You're bang on the button there. Yes, indeed. They have been for a couple of centuries. The Edwardians and the Victorians raved about these things, so it's very true, yes.

Jane: Can I just finish, and again this is a question off the sheet but I'm sure with your immense knowledge you'll be able to handle it, can you just tell me about one Aroid species which listeners will probably never have heard of but that we should know about because they're amazing? Something that you are passionate about that we won't know?

Peter: Wow, that's a broad world!

Jane: Well, just a pick at random.

Peter: Well there's one, actually, which I'm quite excited about. It's a thing my wife Sin Yeng and I describe, it's a genus called Galantharum, and some of the listeners will have heard of this. Galantharum is a small riverside Aroid. It grows on rocky river banks in a fairly remote part of Borneo and it's got white flowers which hang down - rather like a snowdrop, hence Galantharum, Galanthus, the snowdrop - and it's got this incredible vanilla perfume! Now, most people associate Aroids, at best, with the smelling of less than pleasant things! I saw your note about keeping this clean!

Jane: Relatively clean!

Peter: Yes! And that's absolutely right. There's no doubt about it, some of the Amorphophallus from Indochina, the ones with this sort of liquid propane propellant smell, are really pretty hard work to be in close contact with for too long. Galantharum kishii, the name for Japanese collector, has got these incredible white flowers which have got this really nice and very powerful vanilla perfume. This is a plant that I'm very excited about because it was completely unexpected, in the middle of one of our doctoral students' work, a local Chinese student, who's now currently doing a post-doc in Germany, and it sort of popped up literally out of nowhere. Apart from being a very pretty plant and easy to grow, which is rather nice, it changed our perspective on a genus we've been working on and scratching our heads over - a thing called Hotarum, which is also another rather nice Aroid, and Hotarum has got these strange blocks of pollen, the pollen is packed in little white suitcases. We were completely befuddled as to what on earth this thing was related to because nothing else has got this pollen in suitcases. Galantharumsuddenly materialised through a wild collector - yes, this was wild collecting material - and it flowered out and it's got pollen in suitcases. Then, when we did the molecular work, the student did the molecular work, they came out as sisters to each other. So it's a lovely plant, very few people have heard of it, a few people grow it, it smells wonderful, it's got white flowers with a pink tip, it grows easily and, for us, it solved a conundrum! So yes, that would be my choice.

Jane: I love that description of the pollen. That sounds amazing!

Peter: Yes, little boxes. It's incredible, yes.

Jane: As you say, nice to have an Aroid with a pleasant scent, so I look forward to hearing more about that in the future. Do you think it could be something that would be suitable for indoor cultivation in the West?

Peter: There are a few people growing in aquaria, which I have a bit of an issue with, so I know I'm going to make enemies by saying this. I have a slight issue with plants which don't grow underwater in the wild being grown in aquaria, but that's what people like to do, so that's fine. Yes, I have a suspicion that, a bit like Bucephalandra, it proved to be very easy to tissue culture and there's quite a few Buce now being tissue cultured in Europe, which is good news. I have a suspicion that the Galantharummay be in the same category and it grows about fifteen cm tall, tuft of reddy backed dark green leaves on red stems and these white nodding flowers held above foliage. Yes, I think it's got potential, yes.

Jane: That's exciting! Well, thank you so much for joining me today, Peter. It's been fascinating and good luck with the society, the newsletter and all the talks and things that are coming up. It sounds tremendously exciting, so thank you very much!

Peter: Thank you! My pleasure.

[music]

Jane: Thanks so much to Peter and do check out the show notes where you'll find all the information you need, to find out more about the European Aroid Society, and join, and if you do join, there's already a newsletter available for members and a video presentation by Peter about Aroids in the wild.

Patreon subscribers! There are two new things popping up on your Patreon feed of An Extra Leaf, the bonus episodes of the show. One of them is an extra slice of interview with last week's guest, Amy March, of PerkyPlants, where we talk about dealing with the highs and lows of the houseplant social media community. At some point I will also drop a bonus interview with Peter Boyce, where we get further into the world of Aroids, including conservation, plant poaching and loads more. So, Patreon subscribers look out for those and one or two extra bonuses coming while the Patreon is on pause because I'm kind like that!

Now it's time for Question of the Week, which comes from Deborah who wants to pot a handful of cat-friendly houseplants in decorative pots without drainage holes. Deborah asks: "Other than a bed of rocks on the bottom, do you suggest using horticultural charcoal? What would you substitute for the charcoal?" Great question Deborah. Generally speaking, I advise to always have a drainage hole if you can but, that said, if you've listened to the show for any length of time, you'll know I do have a few plants without drainage holes. The main one I can think of is my Episcia** cupreata, member of the Gesneriad clan, which is potted in a square glazed pottery pot and does not have any drainage. It's quite a thirsty plant actually, and it's very easy to tell when it needs watering because it does go rather limp and I tend to wait until that moment to water. The other thing I do, and I would always recommend if you don't have a drainage hole, is calculate precisely, roughly, fairly precisely, how much water it takes to re-wet the potting mix volume in that pot that you're using and only add that much water and then wait until things are pretty dry. So that kind of rules out certain plants that need more steady moisture from this technique because, otherwise, you're going to be landing yourself in trouble if you wait and let them keep drying out to that extent they're going to be unhappy. So I'm thinking of things like a lot of the ferns, things like Fittonias sometimes tend to collapse if you leave them too long. So think carefully about your plant choices.

If you are going to do a pot with no drainage, you do have to think about that bottom layer. Usually that layer will be where the excess water, if there's any excess water that you've put in that doesn't get soaked up by the potting mix, that's where the excess water is going to go. That's going to be your, kind of, water table and, yes, some roots will probably end up growing into that area. In a way, it's kind of a wick-watered kind of method then, because the roots are in there sucking up water as they need them. It does work better for some plants than others. I don't think it really matters what that material is at the bottom of the pot. Normally, I don't recommend putting big chunky crocks and things at the bottom of a drained pot because it actually has been proven that those actually help that substrate and the rocks to hold on to water, rather than improving drainage. Seeing as you don't have drainage anyway, it doesn't really matter, but what it does mean is there's that layer which will be mainly rootless, where that water can sit and the plant can gradually suck up water into the substrate as it needs it. It filters out impurities from the soil. This is often described, rather poetically, as "keeping the mixture sweet"! The idea is that it absorbs things that are going to make the potting mix smell. I don't think this is really true. What it will do, is it will absorb water and nutrients and hold on to them until they're required.

But I think the two things that activated charcoal are doing are: adding extra air to the soil, because it's very porous and there are lots of air pockets in it, and, also, it will take up water and nutrients which can then be released back as the plant needs them. So those things, I think, are positive. I don't believe all the "keeping the potting mix sweet" stuff. I just don't think that is, I don't quite understand the science behind that and I've never seen any evidence that that actually works. I'll link to a good post from LaidBackGardener about using activated charcoal in terrariums, which kind of makes the same points that I've made, really, about why it's not necessary for terrariums.

So, yes, anything that you want at the bottom there that's chunky and porous, so it could be charcoal, it could be expanded clay pebbles. If you put just stones or grit, they will hold moisture between them but not within themselves, so if you can, go for something that's porous. That is worthwhile trying. The main thing with potting without a drainage hole is just being super-careful with the watering, especially at times when the plant is not in active growth. You've got to keep a real hawk-eye on those plants, particularly if you're putting more than one plant in the pot. Make sure the plants' needs are all the same, roughly, in terms of watering because then you won't have one plant that's really fed up because it keeps getting stressed through lack of water, when the other ones are fine. Inevitably in any mixed planting set-up, one plant will out-compete the others. That always just happens. So be prepared to keep an eye out for that and change things as necessary. But, yes, no drainage holes can work, it just requires choosing the right plants and keeping an eye on water quantities and don't worry too much about that layer at the bottom, provided you've got those other things covered.

I hope that helps, Deborah, and I'll be back in September, answering more of your questions! Do stay in touch. I do love all your emails, messages, texts and tips! A couple more that I wanted to share with you before I go, starting with this awesome tip from Jodie, who got in touch about ways to detect when Curio rowleyanus needs watering. This involves the epidermal windows in the globular leaves of this plant, so those are the dark stripes that you see across each of those pea-like leaves and these allow light to go into the centre of the leaf to photosynthesise. Jodie recommends that when the substrate is dry the epidermal windows will close, or become very thin, and that's when it's safe to water. So that's a great tip! I hadn't thought of that, but that's absolutely right! Thank you for sharing, Jodie!

Finally, Lydia got in touch about an under-rated houseplant, Callisia fragrans, the Basket Plant, and is wondering why it's not more widely available? I don't know, Lydia! You're absolutely right, it's a really great plant and we should all be growing it. I think it's one of those ones that gets handed around between friends and family but, yes, Callisia fragrans, the Basket Plant, kind of bomb-proof and a great plant, so let's see more of that around please!

[music]

Jane: That is all for this week's show. I hope that the next few weeks pass painlessly for you all. I will be cracking on with writing 'Legends of the Leaf' and there's still plenty of time to support the book. I need to reach my stretch goal of 115% to unlock a new reward level, which is a really good one! It's going to involve a 25 pack of postcards featuring each of the 25 plant illustrations done by the wonderful illustrator Helen Entwisle for the book. So that's a really good goal. If we can get to 115% I'll be delighted - currently at 109% and I'll keep you updated as to how the book's going and any voucher offers, or so on, as they come up, via the usual social media platforms. Just a huge thank you to all the people, the hundreds of people, who've supported the book. It's been really heartwarming and I'm now on a mission to make this the best, most kick-ass houseplant book out there, so I cannot wait to get this to you, but I'm going to have to make you wait a little bit longer because I've got to finish writing the thing first! Right, that's enough from me for the moment. Go and join the European Aroid Society and I will see you same day, same pod channel in September! Love to you all. Bye!

[music]

Jane: The music you heard in this episode was Roll Jordan Roll, by The Joy Drops, The Road We Used To Travel When We Were Kids, by Komiku and After the Flames, by Josh Woodward. The ad music was Whistling Rufus, by the Heftone Banjo Orchestra. All tracks are licensed under Creative Commons. See the show notes for details.

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Aroid expert Peter Boyce joins me to discuss the newly-formed European Aroid Society, exciting new developments in the world of aroids and why you should never cut the roots off your Monstera! Plus I answer a question about potting plants with no drainage hole.

Reminder: this is the last episode before my six week break over summer 2021. If you want to fill the gap, start here with this page listing all 190+ episodes arranged thematically, plus there’s a list at the bottom of the same page of my appearances on other podcasts.

THIS WEEK’S GUEST

Peter Boyce is a plant taxonomist and biologist based in the Malaysian state of Sarawak, on the northwest corner of Borneo. In partnership with his wife his wife Wong Sin Yeng, he researches aroids, with his current focus on Schismatoglottis - you can see his work on Researchgate.net. He is the honorary president of the newly-formed European Aroid Society (EAS).

Peter mentions various European Aroid growers in this interview: they are the Society’s secretary Enimie van Steenberge (Belgium), website manager Nils Weessies (the Netherlands), board member Geneviève Ferry (France) and president David Scherberich (France). You can see the full list of EAS representatives here. Find out more about the European Aroid Society and become a member here.

Scindapsus pictus with all-green leaves as it starts to climb a tree in Sebangkoi Nature Park (Sarikei, Sarawak). Click to enlarge the image. Peter Boyce.

Check out the notes below as you listen…

What’s an aroid? The flowers are arranged on a finger like structure called a spadix, surrounded by a modified bract called a spathe. Individual flowers on the spadix lack a bracteole, which is unique in the plant kingdom. The spathe and the spadix together make up what’s known as the inflorescence. Check out the EAS’s ‘what is an aroid’ page and the International Aroid Society’s ‘what is an aroid’ page.
Aroid foliage - especially that of the climbing aroids - is very variable according to the age of the plant and its situation. For instance Scindapsus pictus foliage only displays silvery markings when the plant is young and growing on the ground: as it begins to climb, the leaves change to plain green. So keep S. pictus plants cut back when they get big to keep the juvenile foliage.
Rhaphidophora tetrasperma grows in Peninsular Malaysia and southern Thailand, usually associated with limestone. IT is sometimes mixed up with R. pertusa.
Most climbing aroids, including Monstera deliciosa, produce two kinds of roots along their stems - a short, clasping root for clinging onto their chosen support, and as they grow further, they start to produce much longer feeding roots which either travel down the tree trunk into the ground, or hang in the air. The latter don’t have a clasping role: instead they access water and nutrients for the plant. If you are growing in a pot, make sure the hanging roots go into the potting mix. Don’t cut them off as they will simply proliferate.
When supporting climbing aroids, Peter suggests avoiding tying vines to bamboo canes or trellises - instead use a totem of some kind that allows the plant to clasp onto its support. Moss poles, cork strips attached to a pole or a batten of rough wood all work well.
Aroid taxonomy is changing - with researchers working on a new taxonomic framework expected soon that should clarify the relationships between different aroids. More news on this as I get it!
Intrigued by my mention of the different forms of the leaves of Hedera helix? Here’s a column by my friend Alys Fowler on the subject.
The aroid species you probably never heard of is Galantharum kishii, an aroid that grows along riverbanks: its white dangling flowers that have a pleasant vanilla scent. See below for a picture.

See below for more images of aroids discussed in this image. All photographs are copyright Peter Boyce. Click on individual images to enlarge.

QUESTION OF THE WEEK

Deborah got in touch to ask whether horticultural charcoal is worth adding as a base layer to pots with no drainage. The idea that charcoal keeps substrates ‘sweet’ doesn’t seem to have any foundation in science, but it can help to store water and nutrients, which is a useful function in a pot with no drainage. But you don’t have to use charcoal - expanded clay pebbles (LECA) is just as good. If you use gravel or rocks, they will work but won’t hold water as they aren’t porous. Check out this post from Larry Hodgson about using charcoal in terrariums (effectively a pot with no drainage) and why it’s not necessary.

Want to ask me a question? Email ontheledgepodcast@gmail.com. The more information you can include, the better - pictures of your plant, details of your location and how long you have had the plant are always useful to help solve your issue!

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