Endoparasites I have KNown : Pilostyles thurberi (cucurbitales)
Pilostyles thurberi might be one of the most bizarre plants (I know I say that shit all the time - there are a lot of bizarre plants) in North America. It spends 99% of it’s life living INSIDE another plant, only emerging to flower. This is a characteristic called being “endoparasitic”, and my only other experience with an endoparasite was the plant Tristerix aphylla which is an endoparasite of columnar cacti in the genera Trichocereus and Eulychnia in Chile.
When Pilostyles decides it is time to flower, little clusters of tiny mahogany flowers with white interiors burst out of the epidermal tissue of the host plant. In the case of the plant I saw in West Texas, the host plant was Dalea frutescens but Pilostyles can also parasitize the genus Psorothamnus or a few other plants in the tribe Amorpheae of the Pea Family, Fabaceae.
It was long thought that Pilostyles was related to another parasitic plant, the genus Rafflesia which occurs in humid jungles of Southeast Asia, yet DNA sequencing later proved this to not be the case. It turns out that Pilostyles is more closely related to cucumbers and squash (order Cucurbitales) than it is to Rafflesia. Pilostyles thurberi is dioecious, so individual plants either produce male or female flowers. At this particular remote location in Sutton County, Texas, there seemed to be 4 or 5 individual plants in a single, small population of Dalea frutescens.
As far as the genus itself, whats equally bizarre is its distribution - there are 11 species of Pilostyles (with a new one being described in Colombia) and they are widespread. Australia has its own Pilostyles species as does the Middle East, reportedly. How exactly does a genus become so widespread? Is it just an old lineage that evolved before continental drift had placed the continents at their current location? Was it dispersed by some now extinct bird sometime relatively recently (ie the last ten million years)? And how does Pilostyles get around and what do the fruits look like and how do they germinate on the host plant? Does the host plant suffer any ill effects as a result of the parasite (most hosts here appeared to be robust despite the drought and despite being infected with Pilostyles)? Is it possible to cultivate Pilostyles if you’re already growing the host plant? How did something like this evolve (ie were there a specific set of environmental conditions or mutations that made parasitism more adaptive then just doing what most successful plants do - growing prodigiously and producing abundant fruit?
These are the paths my mind always goes down when my curiosity descends on a new taxon. There are so many questions to ask and every answer will seemingly only open up ten more questions.
