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
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A. peruvianum gametophytes, in a somewhat
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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.
