28/03/2023
Parasites!
Normally when people think of parasites, images of insects and little critters in our bodies come to mind. However, parasites are not limited to the animal world!
Parasitic plants are a large group of plants (~4,500 species; 1% of all flowering plants on Earth) that pe*****te another host and 'steal' water, nutrients, and energy. Interestingly parasitism has evolved 12 separate times; at 12 points along the evolutionary history of flowering plants, groups stumbled upon parasitism as an effective way to survive. This is incredibly weird and cool!
In Taiwan we have a number of species of parasitic plants - if you go to the coast you will certainly see "Cassytha", growing in a web of yellow-ish green threads all along the coast line (look for the colour, and follow some of the vine-like branches....you will soon notice that there are no leaves! No need! They are stealing everything from their hosts).
One interesting genus is Balanophora. Below are photos of one of the more cryptic - hard to see - species: Balanophora fungosa subsp. fungosa.
This parasitic plant will flower December to March. This means that the flowering season is almost over, but its not over for the plant entirely. See those yellow 'bulbs' at the top? That is the female flower section, and each plant will have nearly 500,000 flowers, and therefore eventually 500,000 seeds!
When the flowering season is over, those flowers will turn to seeds, and those seeds will be dispersed into the soil and await the right time to germinate.
But...when is the right time?
Actually, we dont know. We *do* know that most parasitic plant seeds do not respond to normal abiotic conditions to induce germination, unlike other angiosperm seeds. For example, rain, cold, heat, dry periods (or a combination of multiple).
If parasitic plants germinated after rains or in response to extended dry periods, they would possibly germinate in the wrong place - not near a potential host tree. This is what ecologists call "su***de germination"; germinating without any chance of survival.
Recent studies have shown that parasitic plants are actually able to sense the chemicals released by trees - "strigolactones" - and use this, and ONLY this, stimulus to germinate. In this way, we can say that parasitic plant seeds are able to sense when a potential host is near, and only then germinate and start growing and feeding off the host!
However, is this happening for ALL parasitic plants? We are not sure yet, but ongoing research in Taiwan and across the world is hoping to find out.
If you are outside and see weird mushroom-like plants growing at your feet, perhaps you could ask them? :-)
