Episode 297: passion flowers as houseplants

*Passiflora citrina* is one of the passion flower species that grows well on a sunny windowsill. Photograph: Pick him! on Flickr.

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Transcript

[0:00] Music.

[0:15] Jane Perrone Do you have a passion for flowers? Well you need to be growing passion flowers. That's right, I went there.

[0:24] Music.

[0:29] Jane Perrone Hello, my name is Jane Perrone and I'm the host of On The Ledge and in this week's show I talk to Rebecca Hilgenhoff about this underrated group of houseplants and how to grow them. Plus I answer a question about a happy hoya that won't flower.

[0:48] Jane Perrone How the heck are you? I hope that your week is proving fruitful. I just discovered I have onion white rot on my perennial Welsh onions, so that's made me a little bit sad. But on the more positive side, I've just got back from another day spent at Walton Hall in Warrington on the Tillandsia plant trials that I'm involved with for the RHS and just a quick snippet of fascinating information about Tillandsias that I didn't know. So have you seen those Tillandsias with the bulbous bottoms? So I'm talking about ones like bulbosa and butzii and Caput Medusae. Well here's the fascinating fact. Did you know that like other house plants that we grow these are what are called myrmecophytes? That means plants that have evolved to have an association with ants. And the ants live in the leaf cavities in that bulbous part of the plant. The ants help to remove or challenge the herbivores that might be eating the plants. And in turn, the Tillandsia provides a home for the ants known as domatia. The ants also leave their fecal deposits on the plant, which then the plant can turn into nutrients.

[2:09] Jane Perrone So, so far, so interesting. But what's the new fact? I asked a question about these bigger, more bulbous plants, whether there's a greater risk of rotting if people don't water them properly. So if you have grown Tillandsias, you know they need to be misted or wetted, but then you need to make sure that water doesn't sit on the leaves so they rot away. And I was wondering whether this was more of a problem in these bulbous species. Species and John Henshaw from Croston Cactus, John is now retired but still but has a major interest in Tillandsias and is also part of the judging panel for the trial, told me that the ants will make a hole in the bottom of the bulbous part of the plant to allow themselves to move around and this can help with drainage. Fascinating stuff, I need to do a whole episode about ant plants than our house plants, because there is some really amazing stuff to find out. I just need to figure out who I need to speak to. So if you can suggest anyone who's an expert in these mamecafites, let me know.

[3:17] Jane Perrone Anyway, on with today's show, I will be coming back to Tillandsias again because I'm involved in this fascinating trial and I'm learning loads. But for the moment today, we're talking about passionflowers, the passive flora genus, which I think many of us think of more in terms of plants outside in the garden, these rampant vines that produce these amazingly intricate and beautiful flowers. And today I'm glad to say we're going to be exploring the ones that work in the house. Yes, you can grow some of these as houseplants. And I'm joined by somebody who is a real expert in this field. So let's get cracking with today's interview.

[3:58] Music.

[4:06] Rebecca Hilgenhof My name is Rebecca Hilgenhof. I'm a botanist slash horticulturist. I'm currently working at the Royal Botanic Gardens Edinburgh. And at the moment, my research is focusing on the nightshade genus Solanum, but I'm also slowly but surely starting to work on my favourite genus, which is Passiflora.

[4:25] Jane Perrone Fantastic. Well, this is what we're here to talk about, passionflowers. I think I've had a few requests over the years for listeners to talk about passionflowers and passionflowers as houseplants. I have to admit, I've grown them in the garden, but never indoors. So let's get into this. What are passionflowers? Where do we find them in nature? And why are you particularly passionate about passionflowers?

[4:50] Rebecca Hilgenhof The genus passionflower is part of the passionflower family, Passifloraceae. It is the largest genus and encompasses more or less 600 species currently. Those of you that know passion flowers, they mostly tend to relate sort of perennial herbaceous vines or even woody liana, depending where they're from. There are also some sort of more or less scadent shrubs that people don't tend to know about, if you are even trees, and also one annual belongs to this particular genus. They come from mostly the Neotropics, so from as far north as the US. All the way through to Central and South America, where the most species diversity can be found. But also we find a small group of species in Southeast Asia, as well as Oceania.

[5:38] Jane Perrone Wow. So I can't believe there's a tree, but just let's roll back a bit. Let's explain for listeners who don't know, you mentioned woody lianas and scandent shrubs. Can you just break those terms down for us?

[5:50] Rebecca Hilgenhof So what most of these plants need is climbing support. So they tend to try to reach the higher light levels and sort of heavily forested areas. And in order to be able to do so, because structurally they're not able to do that themselves, they have tendrils. So vines sort of emphasizing we don't have any woodiness and they're relatively herbaceous throughout, where plants even can experience dieback at certain seasonality. Whereas lianas, for example, they are more like the sturdy, the tough ones that have woodiness as well. So again, we find these sort of in forested areas. And it's quite interesting, I've been previously on trips, and often you can see just this complexity of sort of woody stems and maybe some of them are passive floras but you don't really can't be distinguished that until you see the leaves which is rather difficult so so yeah they're so they're woody um they're woody lianas or herbaceous vines but as I said, they're also tendrilate, meaning they have a modified inflorescence, the tendril that helps them to attach themselves on climbing structures such as other plants or where we grow it in our home but bouquins or you name it.

[7:00] Jane Perrone It's interesting isn't it, I remember learning that in my rhs level two that the the nature of what a tendril actually is - I mean I guess when you don't really when you're not doing a botany course you don't really think about well what actually is a tendril, but it's interesting to know that it's a modified inflorescence rather than a modified leaf or a modified stem i guess. But they're vital, aren't they, because that's what gets that plant kind of clambering about and clinging onto things. But I guess the thing that really sets these things apart, this genus apart, are the unique flowers that, And I'd love to dig into why the name has been applied to this plant.

[7:43] Rebecca Hilgenhof Before I forget, because you asked me what really got me interested into these plants, and I got to say, I love pretty flowers! And they really are exactly what I expect a pretty flower to be like. They have this really intricate floral structure, and particularly being defined by the corona, which is, sort of, a central structure that sits in between the sepals and the petals and the reproductive structures and filamentous, sort of appendages that arise in between what we call the androgynophore and the sepals and the petals. But just to give you an inside out explanation of what the flora structure is like. So, if we start from the outside, so passion flowers are suspended by an often large and showy bract and a bracteal. Then passion flowers also have a hypanthium, which is a floral tube, which in some species is rather minute, but also there are some other species which come from the high Andean mountains in Ecuador, Colombia and Peru, which can have floral tubes up to 20 centimetres long, for example. These are then followed by the petals and the sepals, which are in fives. And then as I previously mentioned this really conspicuous row of filaments which we call the corona and then following to the corona, other reproductive structures are also known and it's very specific to actually the Passifloraceae family and of course the genus Passiflora which is the androgynophore which is sort of a fusion of the androecium and the gynoecium, so the male and female parts, and what really is interesting and if people don't know what the passion flower flower looks like, I really highly recommend now to just go online, google the flower so you can just follow what i've just been explaining but also this intricate floral structure uh lets the first sort of spanish missionaries that came in the 15th and 16th century to adopt this very unique structure of the plant in general but specifically the flower plants as a symbol of the last days of Jesus Christ, especially his crucifixion. Hence the common name and even the Latin genus name Passiflora or passion flowers, because it relates to the passion of Jesus Christ.

[10:01] Jane Perrone It's a fascinating flower. I will put some pictures in the show notes for people to have a look at while they're listening, because this flower is intricate to the max. If somebody said to you, oh yes, somebody has created this as part of a fantasy novel or a fantasy film as being an alien flower, you'd go, oh yeah, right. If you'd never seen one before, you would not believe that it's from planet earth because it is just so elaborate. And I think that's what draws lots of people into these flowers, isn't it? They're just so intricate. I'm presuming, though, that from the plant-centric point of view, there are some very good reasons for all of these structures?

[10:41] Rebecca Hilgenhof Yeah, very much so. It obviously has got a lot to do with pollination and the different pollinators that these come across in their native habitat. And you have got three major groups of pollinators as well, which are largely insects. I mean, when I speak about that, we know examples of some species but there's a lot that's not known, so I'm going to talk quite generalistic in that sense. But the passion flowers that tend to have large coronas and are sort of bluish white or purple-coloured, they are thought to be pollinated by large neotropical bees and the corona filaments which, you know, in many ways are quite colourful, they're sometimes stripy, they sort of are an attractant for the insect, but equally also serve as a landing platform. So when you think of, like, a large, sort of bigger than bumblebee-sized neotropical bee trying to approach the flower, so that's what's helping them to sit where they're supposed to be and then obviously what the plant wants is to pick up the pollen and deposit it on the stigma of the next flower. However, aside from the large-flowered species, we also have some really small-flowered passion flowers, sort of the corky passion flower, which is quite a well-known species, quite an invasive species in some countries, in fact, and it's got really small, greenish flowers and these flowers are apetalous, so they're lacking the petals entirely. And these sort of species are thought to be pollinated by much smaller insects, such as ants, wasps, and even flies. Although again, the smaller the insect, the more difficult it actually is to prove if they are the pollinators. But these are the two, sort of, large insect groups that we think pollinate Passiflora. And then the second group I'd like to mention are birds. I've already mentioned that passion flowers have a hypanthium and then in some species that can be rather large. And the reason why we have hypanthia that grow up to 20 centimetres long is due to the bird pollinators, which are hummingbirds. So, obviously, hummingbirds are largely neotropical distribution and there are some that have really, really large beaks. And so, the size of the hypanthium in most species equates to the length of the beak of the hummingbird pollinator. So this concerns a lot of the types of what we call taxonia species that occur in the sort of Ecuadorian, Colombian and Peruvian Andes. But also I should mention that although hummingbirds are sort of the main bird pollinator, we do have a group of Oceanian species, I mentioned a few occur in Oceania, and particularly Australia, that are pollinated by sunbirds, and that's really interesting. They do not have a hypanthium, but what they have, they have the interior row of the corona, which sometimes we call also the operculum, which is raised. So instead of having a hypanthium that gives them the beak size, it's, in that case, the operculum. So it's sunbirds in, sort of, Australia that do the pollination for them.

[13:45] Jane Perrone Pollination is one of these things that I imagine studying it is incredibly difficult because you've got to get out there in the field and try to see what... I mean, there could be lots of things coming to a flower without actually doing the pollination process. I imagine this is why our pollination information is quite patchy, I guess, because there's so many different species and probably each one has its own method. It's hard to gather that information for botanists who are out there in the field. But it's fascinating stuff to hear that, you know, there's so many different adaptations for different species.

[14:21] Rebecca Hilgenhof Oh, yeah, absolutely. I mean, it's as you said, it's really difficult to say if you don't sit next to a plant for hours and hours and you see a visitor, because a lot of the time we call it a visitation, because until we are sure that the pollen is actually transferred to a flower of the same kind, we don't really we can't really call it a pollinator. And i think there are other ways these days where we can maybe check if we have visitors like you know we can study what pollen grains for example we find on bees and we can relate them uh we can you know analyze them with modern molecular tools and then see but yeah mostly what they've done back in the days and sort of what I find we're really lacking a bit these days is people sitting next to the plant for hours and hours and hours on end and are able to see what at least visits it, so yeah but before we move on to any other question I really like to mention the last and third group because it's really unusual and I think although most people probably see passion flowers they're like yeah I can yeah bees I can see that and birds yeah I can see that too. It's also a third group which are mammals - and when I speak about mammals, it's bats so there's a handful of species that are bat pollinated and probably I should have said that a lot of the bird pollinated passionflowers are red. So we have certain colours that are associated with certain pollinators. And for the bat pollinated species, it's actually white-flowered species. So we've got a lot of white-flowered species. And what is really distinguishing with them is that they do tend to have like big open hypanthia, quite sturdy sort of inflorescence because from what I understand, bats are not the softest pollinators, they tend to quite be harsh when they go into pollination mode to get the nectar for their own means. And so their whites, they have often reduced corona filament. And also another condition that's otherwise very rare within Passiflora is bilateral symmetry. So most of the passionflower flowers are actinomorphic so you've got various planes that you can sort of cut through, whereas bilateral symmetry similar to an orchid - you can only have that one mirrored plane. So for bat pollination that's what some species have adapted to bats being a little bit uh clumsy with their pollination.

[16:37] Jane Perrone Sounds about right I love bats but it's you know people never think of them as pollinators do they but obviously they're playing an important role, particularly in certain climates and certain places. You've talked a little bit about where these plants grow. How wide is their native range? And are there species that are very common in the wild that you'd expect to see everywhere?

Rebecca Hilgenhof If you were in South America, you'd expect to see a lot of them. So we find a couple of species in North America. And I know you've got plenty of listeners from North America, so they're probably familiar with the maypop, which is Passiflora incarnata. And it's also the plant that's sort of medicinally used in teas, helps you sleep, helps you to be calm. But there's another, I think, at least 10, 12 species that are actually native to North America. The hardier species, Passiflora lutea, which occurs nearly up to the Great Lakes, which some people grow here outside in the UK or in Europe. But then also there's species in North America that occur sort of in Baja California, in sort of desert habitats. The most diversity of passionflowers are certainly sort of centered about Central America, but Northern South America. So from I mentioned earlier, we've got about 600 species and the center of species diversity is in the countries of Colombia and Brazil. Brazil, obviously, a rather large country and it sort of makes sense. But if you have a quick look at the map and see it in comparison to the size of Colombia, Colombia really harbors a large species diversity, mostly because it also has... It provides a lot of different habitats. You can find habitats from sort of Amazonian coastal plains, Amazonian rainforests, into high up into the Andean club forest, subalpine habitats that you find in the Andes as well. Then throughout sort of North America, they go as far south as sort of Argentina and Paraguay and even Chile, but they become a bit scarcer because the climate is getting a bit too cold for them. And then, as I said, you have a group of 22 species that are in Oceania and sort of Southeast Asia. So we've got a handful of species that are in Australia and they're sort of in wooded habitats. We have got one species which occurs in New Zealand, which is a dioecious species, which is also really interesting. We've got species in Pambunagini, Fiji, the Solomon Islands, Thailand, Vietnam. But also you can see it's a wide range of habitats, you know, from savannas to rainforests, you name it and that probably has also contributed to the vast species diversity that we see.

[19:09] Music.

[19:18] Jane Perrone More from Rebecca shortly, but now it's time for question of the week and this one comes from Anne-Marie and concerns a very healthy looking hoya - this one belonged to Anne-Marie's mother and is now in her possession. It is super healthy looking. I will put a picture in the show notes for you to check out. It's growing up some bamboo canes and looks lush and lovely. Looking at it I would say I'm not quite sure whether it's Carnosa or Hoya gracilis and part of the reason why we don't know is because it has not flowered. Certainly since Anne-Marie has had this plant. So she's wondering why this huge Hoya has never, to her knowledge, put out any blooms. These kind of questions fascinate me. You've got a perfectly good looking plant that just hasn't done what genetically it should be predisposed to do. Why? Well, we could come up with all kinds of theories for this. I'm going to throw a few out there and Anne-Marie will have to see what makes sense. I suspect that this plant may be a bit too happy. How does that work? Well, Well, of course, plants flower to reproduce sexually. So sometimes it just takes a little bit of jeopardy on the scene to make them feel like maybe they're not doing as well as they might. And therefore they need to reproduce. And with a hoya, sometimes people say that means the plant being a little bit root bound. I find that flowers come quite readily on Hoyas that have had a quite a dry period. Before they come up to bloom so it may be a case of letting this Hoya dry out a little bit more between waterings giving it that little bit of stress that might prompt some flowers just to remind everyone what Hoya peduncles look like. They look like little burnt cigarette ends so Anne-Marie these are the things that you should be looking out for little stalks coming off the main stem them they'll probably be about three centimeters long and they will look like a burnt cigarette end the longer the burnt cigarette end bit the older the peduncle as they are known and that's where the stalks for the individual flowers come from so I would say have a look at your plant see if it's got any of those that's telling you that it has bloomed before and keep an eye on those for signs of growth of the little clusters of flowers because that's where they're going to come from I think the other thing you can do maybe is give this plant a little bit more light sometimes plants won't flower if light isn't strong enough so gradually moving it towards a light source may help too but other than that I just try toenjoy this beautiful hoya which is obviously an heirloom plant, and not worry too much about it not flowering. And it may surprise you at some point but don't beat yourself up over it as long as the plant is healthy that really is all that matters. The other thing worth saying is that if this was a much younger Hoya i would also be pointing out that hoyers sometimes in the case of some species won't flower until they're anything from like two to five years old, so in a younger plant it might just be it isn't mature enough yet so that's worth bearing in mind too. But Ihope that helps Anne-Marie and if you've got a question for On The Ledge, do do drop me a line ontheledgepodcast@gmail.com. And don't forget to check out my other Hoya episodes, which you'll find linked from the show notes at janeperrone.com, where we can go deep into the world of these wonderful vining plants. But now back to my interview with Rebecca about passionflowers.

[23:07] Jane Perrone Now let's get on to these plants as houseplants - indoor growers i'm presuming that not all these species are going to work because but possibly some are too big too specialist in terms of their requirements but what are the species that work best indoors and and can you explain why these aren't more popular as indoor plants?

[23:28] Rebecca Hilgenhof Why they're not more popular i have no idea. i'm gonna go and set out to change i'm glad you invited me for your podcast because I think it's the first step and I'm also hopefully in the future we'll write a few articles about the topic because I think people just don't know the right selection. And I think that really is the main reason they have this reputation as getting too big. Some of the bigger species need to be rather large to flower you need a lot of sunlight to flower these large species um from what i've mentioned about their distribution a lot of them come from tropical areas and then maybe it's something that we may not be replicates to in our sort of windowsill growing arrangements that we have at home maybe in a conservatory on a glass house but not everyone does have that um but I've been you know I'm not originally from the uk but I've been in the UK for 15 years now, I've always studied and my horticulture and botany in the UK and i grew up and I always liked my passion flowers andI always had passionflowers in my window. So I think it's definitely possible if you have the right species. And when we talk about right species selection, there's a large group of sort of small flowered species that are highly recommendable.

[24:37] Rebecca Hilgenhof We talked about earlier, some of them are vines, some of them lianas. Obviously, lianas grow really big, 15, 10, 15, 20 meters. You name it. That's what I said. They're the ones that will need a long time to get to flowering if the light levels are even enough. And they're mostly tropical. So what we really want to do is to look at the smaller species that are vines. So they grow maybe two to four meters long. Obviously, we can do our own work in order to keep them in bay with that. But also the nice thing is that they don't necessarily have to have this vast size in order to get to flowering. Also, sunlight does play a role. So really, a sunny window is always recommendable with passionflowers. But I would look into small flowered species. Obviously, main feature, passionflowers, is the flower. I do not disagree, but there's some really, really, really nice species that have ornamental foliage. I would definitely divide the species into some that I would rather grow for their flowers and some that I would really just grow for the foliage.

[25:35] Jane Perrone If I'm looking for something that maybe has interesting flowers, plus maybe some element of interesting foliage, what species would I be looking out for?

[25:44] Rebecca Hilgenhof So I think I've got two species that we definitely would want to look out for. And just to say, there are nurseries in the UK that breed, that propagate, that offer passionflowers. And the ones that I mentioned, you should definitely find in the UK trade. So the first one, which is my number one, because it's a very unusual species in terms of flower colour, it's Passiflora citrina, the yellow flower, passionflower. It's got vividly yellow flowers, which is really unusual for passionflowers. It's part of a group that sort of produce relatively succureaceous leathery foliage, which also is an adaptation that actually is quite suitable for our houseplant growing. They've got hairy leaves as well. You know, hairy leaves always emphasize that you sort of are a bit more adaptable to more temperate climate. So it's a species that grows native in central and western Honduras, and is also possibly found in adjacent eastern Guatemala and El Salvador in Central America. And there it is found in moist pinewood forests. So it's a bit more of a temperate habitat, which makes it a bit more suitable in terms of windowsill growing in the UK. But really it's a species because it comes from these pinewood forests that bluffs acid soils. So as long as that is provided, it's a species that is relatively pest-free and will flower up to 10 months a year. So they have a small break during the winter season, but as soon as light levels increase in the spring towards the summer months, you will get two really nicely sort of four diameter across yellow flowers. I mean, they don't have the largest corona, but they are certainly a passion flower and one to look out for.

[27:26] Jane Perrone So we're putting this on a really sunny windowsill presumably we'd be using ericaceous compost for its acid loving nature?

[27:34] Rebecca Hilgenhof Yes we could, I mean any sort of potting compost and our potting compost are always a bit on the acid side anyways, I think most of them i think it should be just fine if you want to do an extra nice to your plant then yeah do choose ericaceous compost but actually they're not that fussy.

[27:48] Jane Perrone OK oh that's good to know, and what about moisture levels do they like to stay nice and moist all the time or should we be should we be sort of being careful with to giving them too much water?

[27:58] Rebecca Hilgenhof I don't think there's too much during the summer season and particularly if it's warm so i would say keep it moist throughout the summer the growth season when they produce their flowers but reduce in the winter i mean it's a it's a species that can cope with minimum and but i say can very long because really don't do for too long to four degrees preferably 10 to 12 degrees And obviously, like with any other houseplant, we would want to reduce the water so we don't get any root rot happening.

[28:24] Jane Perrone And is this something that you would be trailing or is it best to give it something to climb up or, you know, giving it any kind of trellis or obelisk or some kind of support? Presumably if it's one of these tendril bearing plants, it's going to want something to grab onto.

[28:39] Rebecca Hilgenhof Yeah, absolutely. So I think the world's your oyster with that. You can use bamboo canes to trail them on. What I always like to do is just have like strings going around my window so they can go have a bit more opportunity and cover in the whole sort of window surface. But obviously, I'm passive flower mad and other people might want to grow other plants there as well. One thing that I would definitely say, do not try to twine them around somewhere. You can always, like when you buy sometimes passionflowers from people or from nurseries that not specialize in passionflowers, they're sort of twining them around this sort of circular structure. But as you said, it's a tendril-like climber, so they really want to find their own support. You can help them along. You know, you can always take the tendril and put it somewhere where it's supposed to go because they never want to grow where you want them to grow. But one thing not to do is really just twist them around. It would be a bit like, you know, someone would twist us around and say, now eat a sandwich and digest. And our digestive system would go really, really bad about it. So passionflowers hate that. And as a result, they will shoot somewhere else. So, you know, if they're not having to die on you because they're actually quite resilient, they will shoot a bit lower down and do their own business anyway. So you may as well go with the flow of a passionflower and do it in the way they want to.

[29:57] Jane Perrone You mentioned citrina there. What would be another option? Species that would work well indoors that you'd recommend?

[30:04] Rebecca Hilgenhof It's a hybrid that i've chosen and it's a foliage plant for me but i really it it needs mentioning it's one of the most beautiful hybrids that i think there is it's called passiflora manta it's a hybrid between Passiflora xiidzodz and Passiflora coriacea and it's a group of passion flowers which we call the batwing passion flowers so essentially they have leaves that are shaped like a batwing with two sort of very large multilateral lobes. It's a hybrid I produced in 2002 by a good friend of mine, Maurizio Vecchia, in Italy. So he was given the name Manta because it actually looks like a Manta, right? But the leaves, they're very coriaceous. So again, you know, has a sort of a more physical attribute that I think makes it very suitable for a windowsill growing plant. They're really shiny and glossy, but they have this beautiful variegated pattern throughout. So they go from when they're immature to a light green into more of a dark green and have that, as I said, this really sort of light green, whitish variegation. So it looks beautiful, really dark stems behind it. But also the flowers are really quite nice too. I do really like them. They are about sort of two and a half centimetres across and are greener, sort of greenish and yellow with a bit of black. Also a petalus, like in the petals, but nevertheless a really, really nice showy little flower. But as I said, it would be for me one of the ones that I would consider a foliage plant. It too is relatively pest resistant, can curb upper temperatures to down to 10 degrees. You know, we have that it's a hybrid. We do have a bit of hybrid vigor there going on as well. So it really makes the perfect indoor plant.

[31:43] Jane Perrone Sounds great. Now, I must ask this question because I know some listeners are going to be thinking it, which is, obviously, we've all heard of passion fruit. We've probably eaten one or two in our lifetimes. Do passion flowers produce passion fruit? And is it possible to grow something that's edible from your passion flower indoors? I'm guessing the answer is no, but I kind of want to, I've got a dream here that maybe I'd need a lot of grow lights.

[32:11] Rebecca Hilgenhof I think your dream is possible with a lot of grow lights and a lot of humidity indoors so, most passion flowers are edible most of them are not tasty there is enough that are really tasty and that includes species like the banana passion fruit or also known as caruba it's passiflora mulissima and tripartita then we have our purple passion fruit the one that we are sometimes here see in Tesco or another supermarket which is the purple passion fruit also known as gulupa it's Passiflora edulis form edulis sometimes you also find the yellow form which is former flavicarpa in our markets but unfortunately passion flowers are quite underrepresented and those slotted that i just mentioned are very acid so the first one the caruba the banana passion fruit very sweet but you can only find it in the andean regions when you go on a holiday or on a field trip to see Pasiflorus. But then also a bit that extends your range of what you can eat. There's one passion fruit called the sweet granadilla, which is Pasiflora ligularis. It occurs in Northern South America. Sometimes you can find it in Dutch markets because of Suriname. So they're importing it over from Suriname. But unfortunately, it's something that we never see. And for me, it is the most delicious passion fruit that I know. No, absolutely sweet, juicy, and delicious. Unfortunately, as I already said right in the beginning, the ones that we do grow at home, if they produce fruits, then... And that's questionable as well, right? Sometimes you, or most often you need two different clones, so we may not have two different clones, then that's very difficult. And for example, the Passiflora caerulea that we've mentioned earlier in conversation, which is the blue passionflower, which we can grow outdoors. It's an edible species. It does not taste well at all. And I should also say, before I finish up the topic of passion, fruits is, although a lot of them are edible, there are one or two that are toxic as well. So really you ought to know what you're eating as well.

[34:17] Jane Perrone Yes that's a good point - because there's a few houses around where i live that have got really big passion flowers and they have blue flowers and then these bright orange fruits would that be the caerulea that i'm seeing then?

[34:30] Rebecca Hilgenhof Yes that's the caerulea indeed.

[34:31] Jane Perrone Yeah i mean i often look at them and think they look so delicious how can they not be delicious but then again as i say if they're just kind of um a bit tasteless Because I'm imagining in the wild, monkeys and birds and various animals are thoroughly enjoying them. But just because they're not nice for humans doesn't mean that they're not a valuable crop for somebody else, right?

[34:51] Rebecca Hilgenhof* Absolutely, absolutely. But I think, you know, never say never on passionflowers. One thing is for sure, they're easy to hybridize. And people love hybridizing passionflowers. So if people are interested, t here's a website of the Passive Flower Society International, where they're looking after the cultivar registrar. So I think if we go forward in the future, although they're mostly bred for their flowers at the moment and the ornamental aspect, I wouldn't be surprised that maybe in the future we find some suitable indoor plants that maybe even produce some fruit.

[35:21] Jane Perrone On the podcast at the moment is my sow along. I'd just be interested to know if seeds of any passionflower species are available commercially to buy so that people could maybe grow them from seed. Is that something that's on option?

[35:34] Rebecca Hilgenhof Yes, definitely available. I wouldn't know exactly where to look out for, but it's about looking on the internet and see what's available. But they're easily propagated from seeds. I mean, also easily propagated from cuttings, but certainly seeds is very straightforward. Like with many plants, you know, the fresher, the better. They do have what I would say when we're talking about seeds, the seeds of a passion fruit encompassed by an aril, which gives us the juicy fruitiness that we so much enjoy. But it also has inhabitants that prevents germination. So if someone gets some seed that maybe not that clean, make sure you get clean them out before you put them in some soil.

[36:15] Jane Perrone Yeah, I think tomatoes are the same, aren't they? That's that sort of a layer of, I'm going to use the word mucilage. It's probably not the right word, but yeah, that's a good point. But I mean, I'm sure there'll be listeners out there who've given that a try and always worth experimenting with seeds. But that's been absolutely fascinating, Rebecca. Thank you so much for sharing your expertise. I'm sure you've inspired some listeners to think about passion flowers for that sunny windowsill because they're so beautiful. Thanks so much for joining me, Rebecca.

[36:45] Rebecca Hilgenhof Thank you very much for having me.

[36:47] Music.

[36:52] Jane Perrone If you want to delve further into the world of passion flowers do start with the show notes at janeperrone.com where you'll find images of some of the plants that Rebecca's been talking about books andacademic papers you might want to read and Rebecca's social media info so do go and checkthat out. And if you're a Ledge End or Superfan, if you're subscribed to my Patreon, then you will be able to access an extra bonus interview with Rebecca all about the fascinating pollination strategies of these plants. That's available now in An Extra Leaf number 126. That's all for this week's show. I will be back now in two weeks time. That's two weeks from now. so until then love your plants love yourself and remember every time you spread the word about on the ledge your hoya gets another peduncle bye, the music you heard in this week's episode was roll jordan roll by the joy drops The Road We Used to Travel When We Were Kids by Komiku and Whistle by Benjamin Banger. All tracks are licensed under Creative Commons.

[38:18] Music.

Host Jane Perrone talks to botanist Rebecca Hilgenhof about passion flowers, finding out which ones we can grow as houseplants. Plus the Q&A tackles a question about a Hoya that refuses to bloom.

This week’s guest

Rebecca Hilgenhof is a botanist at the Royal Botanic Gardens Edinburgh and she specialises in Passiflora & Solanum research. You’ll find her as @passifloratree on Instagram.

Patreon subscribers at the Ledge End and Superfan level can hear an extra interview with Rebecca in which we discuss the fascinating pollinator relationships formed by different passion flower species in An Extra Leaf 126.

Passionflora ‘Manta’. Photograph: Rebecca Hilgenhof.

Check these notes while you listen…

Passiflora is a genus of plants native to parts of North and South America, Oceania and Southeast Asia.
The passion flowers Rebecca recommends for growing indoors are Passiflora citrina (pictured at the top of the page) and P. ‘Manta’, pictured left.
Not all passion flower species produce fruit that is edible for humans, and some may be toxic.
If you want to know more about passionflowers, consider joining the Passiflora Society International (PSI) – Passiflora Society International (PSI).
Rebecca suggests these books on the subject of passion flowers:
Farbatlas Passionblumen – Colour Atlas Passionflowers, Ulmer and Ulmer 2005
Passiflora: Passionflowers of the World by Ulmer and MacDougal 2004
Passion Flowers 3rd edition by Vanderplank 2000
Passionflowers by Boender 2019
She also recommends the following papers if you are interested in the Passiflora genus from an academic point of view:

de Castro, É.C., Zagrobelny, M., Cardoso, M.Z. and Bak, S., 2018. The arms race between heliconiine butterflies and Passiflora plants–new insights on an ancient subject. Biological Reviews, 93(1), pp.555-573. 2017_Biol_Rev-libre.pdf (d1wqtxts1xzle7.cloudfront.net)

Abrahamczyk, S., D. Souto-Vilarós, and S. S. Renner. "Escape from extreme specialization: passionflowers, bats and the sword-billed hummingbird." Proceedings of the Royal Society B: Biological Sciences 281.1795 (2014): 20140888. Escape from extreme specialization: passionflowers, bats and the sword-billed hummingbird | Proceedings of the Royal Society B: Biological Sciences (royalsocietypublishing.org)

Jørgensen, P.M., Muchhala, N. and MacDougal, J.M., 2012. Passiflora unipetala, a new bat-pollinated species of Passiflora supersect. Tacsonia (Passifloraceae). Novon: A Journal for Botanical Nomenclature, 22(2), pp.174-179. 41811673.pdf (jstor.org)

question of the week

Anne-Marie got in touch about her mother’s hoya which hasn’t flowered. As you can see from the picture, it looks very healthy but doesn’t seem to want to put out any blooms. I suggest a couple of possible explanations for this: it’s always hard to say why a plant hasn’t flowered, particularly in the case of a Hoya that can live for decades.

Sometimes with Hoyas, they haven’t flowered because they aren’t mature enough. Some species don’t flower until they reach five, seven or even older. That doesn’t seem a likely issue in this case, but it’s worth knowing if you have a younger Hoya that hasn’t flowered.

I suggest that Anne-Marie’s Hoya may need a little more stress in order to flower - I find that many Hoyas bloom really well after being left to dry out for longer than usual. This is because sexual reproduction is the plant’s way of ensuring its survival - and sometimes this isn’t triggered unless the plant feels as if there’s no risk of it dying. Some Hoyas are also reputed to flower better if they are ‘snug’ in the pot, in other words, somewhat rootbound, which effectively is the same thing.

This Hoya may also benefit from more light, and this may make the plant produce some peduncles - so I suggest Anne-Marie gradually moves is a little closer to the window if possible.

Anne-Marie can check if the plant has flowered before by checking for peduncles, which are the flowering stalks from which the flower clusters emerge. The peduncles stay on the plant from year to year between flowerings, so do not cut them off! They look like this - I liken them to a burnt cigarette end (the longer the burned-looking bit, the older the peduncle).

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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