In cultivation, plants known for iridescence such as S. uncinata can show more or less of this colouration under different cultural conditions: I find that the best conditions for S. uncinata are moist, shady and humid (my default conditions for the genus). In bright light, this plant will blush pinkish-red, which can create a spectacular effect coupled with the iridescent blue, though it is a fine line to achieve both and maintain both colours. Apparently the ratio of red to far-red light makes a large difference in the production of iridescence, at least in the related species Selaginella willdenowii., though that`s somewhat outside the realm of the casual grower to play around with.



But perhaps the most intriguing aspect of this whole thing is the why: what evolutionary benefit do plants gain from this colouration? A paper published in the Journal of the Royal Society suggests two possible advantages: the iridescence may act as a deterrent to herbivores, as the (seemingly) constantly changing shape would not allow herbivorous insects, for example, to develop a search image (a familiar shape which the insect recognizes as a food source: search images abound, in our own minds as well as those of insects). The other possible advantage is that the iridescence (which is primarily seen in shade-dwelling plants, as I mentioned earlier) can prevent damage from exposure to too much light, say from a newly created hole in the canopy overhead that permits direct sunlight to reach the forest floor.



Whatever the reason, these plants hold a special fascination, and they are beautiful to behold. With a little care, these can make incredible additions to anyone’s indoor garden (and outdoor garden, if you are fortunate to live in a place with mild enough winters to get away with it).