Nature and Science - houseplants 🌿
Since this week is a free week, I wanted to talk about something that I am passionate about – plants!
I started collecting houseplants quite a few years ago, but my passion for it really exploded over the last few years as I really got the hang of their care. I’m sure many of you can relate, as the houseplant trend has really exploded over the past year or so due to people taking up new hobbies during Covid-19! I wanted to focus on a small part of my collection, linking nature interpretation to the science and explaining a bit about how the genus hoya has grown into an ever-expanding cross breeding frenzy for collectors.
A photograph of a Hoya carnosa taken by Doug Chamberlain (n.d.) taken from Vermont Hoyas.
The plant seen above is called a Hoya carnosa, and is one may remember trailing around their grandparent’s house, as it has been widely available and popular for decades. Hoyas can be identified by their thick, waxy leaves, and their unique flowers that emit a variety of scents depending on the species ranging from floral to fruity to musty. The flowers erupt from the tips of pedicels from the spur on a peduncle, into an umbel shape. Hold on…what do all these words mean??
A photograph of a peduncle (L) and a spur ® taken by Summer Rayne Oakes from Homestead Brooklyn.
A peduncle is a stalk that bears a fruit or a flower – you may have heard people refer to the pumpkin “handle” as a peduncle – because that’s what it is!
A spur is the part of the hoya where the new blooms erupt from
A pedicel is a small stem that attaches the actual flower structure to the rest of itself
An umbel shape is a flower shape where all the pedicels attach at a common point and spread out like an umbrella – if you’ve ever seen common milkweed, this firework like shape is an “umbel” shape.
A photograph of Asclepias syriaca (Common milkweed) showing the umbel shape, taken from Wikimedia Commons.
Fun fact - despite hoyas originating largely in tropical areas and milkweed being found even here in North America, they share this structure because they are part of the same taxonomical family (Apocynaceae).
A photograph taken by Dave Chamberlain from Vermont Hoyas showing a Hoya serpens (L) and a Hoya ‘mathilde’ ®.
Now onto the interesting part. Hoyas are an enormous genus, with a huge variety of species that vary in size, shape, colour (both for the leaves and the flowers), and care requirements. Many of the species have been purposefully cultivated to maintain a certain look, but many have also cross pollinated naturally in the wild. One example of this is Hoya ‘Mathilde’ (seen above on the right) which is a cross between a H. carnosa and a H. serpens, resulting in the thick green carnosa leaves and the attractive round shape of serpens.
A photograph of a hoya flower cluster, individual flower, and cross section of a flower taken from Mochizuki et al. (2017) showing the structure of a flower and the location of the pollen.
Despite being a long-loved genus, little is fully understood about the pollination of hoyas, and many new species born from cross-pollination occur by accident by insects. The flowers on hoyas are complex and specialized, as seen in two studies by Mochizuki et al. (2017) and Landrein et al (2020), where H. carnosa and H. pottsii were found to be pollinated almost exclusively at night by a select few large species of moth. Furthermore, Landrein et al. (2020) attempted to hand pollinate their hoyas but found it to be difficult and required a microscope. The trouble with these plants is that the pollen is not readily exposed but is actually hidden within the flower in little sacs that need to be fully removed (as seen below marked with “po”).
A photograph of part of my hoya collection (L) and a newly forming bloom ® on a Hoya lacunosa.
Seen above is a sample of my little collection of hoya, including a bloom starting on my H. lacunosa. I am hoping to try and get some seeds from it by using the same techniques used in the paper mentioned above! Since it is the only bloom coming right now, there isn’t a way for me to cross pollinate to try and make a new species, but I am hoping that in the future this will be a possibility.
I would love to hear from anyone else who keeps plants from this awesome genus, or anyone else’s plant stories from quarantine!
Works Cited:
Chamberlain, D. (n.d.). Hoya Carnosa. Retrieved from Vermont Hoyas:
https://vermonthoyas.com/hoyas-c-d/hoya-carnosa/
Chamberlain, D. (n.d.). Hoya Serpens. Retrieved from Vermont Hoyas:
https://vermonthoyas.com/hoyas-s-z/hoya-serpens/
Chamberlain, D. (n.d.). Hoya Mathilde. Retrieved from Vermont Hoyas:
https://vermonthoyas.com/hoya-cultivars/hoya-cv-mathilde/
Landrein, S., Zhou, Z.-Y., & Song, S.-J. (2020). Pollinators of Hoya pottsii: Are the strongest the most effective? Flora, 1-10.
Mochizuki, K., Furukawa, S., & Kawakita, A. (2017). Pollinia transfer on moth legs in Hoya carnosa (Apocynaceae). American Journal of Botany, 953-960.
Oakes, S. R. (2019, April 11). The Ultimate Hoya Care Guide. Retrieved from Homestead Brooklyn: https://homesteadbrooklyn.com/all/2019/4/8/the-ultimate-hoya-care-guide#:~:text=The%20flowers%20of%20hoya%2C%20which,)%20or%20flat%2Dtopped%20surface.
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