I recently noticed, to my great excitement, that some fern spore had germinated in one of our vertical gardens. In this case the species in Adiantum peruvianum, the Peruvian maidenhair fern, a delightful species with unusually large pinnules (leaflets), and which eventually grows fronds a metre long in ideal conditions. When this species was planted, the fertile fronds were already showing the sori (clumps of sporangia which produce the spore) along the margins of the pinnules, and I had hoped (and had really thought it was against the odds) that some of the spore would in fact do its thing in the garden. Lo and behold, here we are.
You may know that the ferns are a fairly primitive group of plants that were on earth a million years before the dinosaurs, having only a rudimentary vascular system and never having developed flowers or seeds. In the right conditions, propagation by spore seems to be an extremely effective means of reproduction, provided a few basic needs are met.
In flowering plants, a seed produces a plant which grows to maturity, produces male, female or dioecious (male and female) flowers, pollinates and/or is pollinated, and the pollinated flower then produces seed to complete the cycle. In ferns and other spore-producing plants (mosses, liverworts and tree ferns), spore germinates and produces a gametophyte consisting of a single simple leaf called a prothallis. It is the gametophytes which do the reproducing in these plants: the male organs of the gametophytes release sperm, which, dependent upon the presence of a film of water on the surface of the growing area (certainly one of the reasons why these plants are usually restricted to moist, humid environments), travels between gametophytes and fertilizes the female organs. At this point a new plant is produced which is immediately more recognizable as a fern, and which will reach maturity and itself produce spore to complete the cycle. Colonies of gametophytes can apparently continue to produce ferns for some time, so in cultivation plantlets can be removed and the colony left to continue to reproduce, which is a pretty good deal.
With my little A. peruvianums, the first part of the cycle is complete (although perhaps it's difficult to call a part of any cycle the first part). What remains to be seen is whether germination can be achieved: the outermost layer of the garden material does not have the constant film of water that the habitat of A. peruvianum does, but I am attempting to keep the area as moist as possible in an effort to assist germination. Here's hoping for a favourable outcome; the little gametophytes certainly do add an interesting element to the garden, though, at any rate.