Wildlife Gardening in February

N.B. If your new to David’s monthly column then please be sure to read the ‘setting-the-scene’ opening piece first.

An Insight into the less-fashionable plants

Wheat grain. Endosperm shown, this is ‘flour’ and is used up when the seed germinates and forms no part of new plant. The other bits are the seed, with one cotyledon (seed leaf) and root / stem also shown.

Wheat grain. Endosperm shown, this is ‘flour’ and is used up when the seed germinates and forms no part of new plant. The other bits are the seed, with one cotyledon (seed leaf) and root / stem also shown.

I’m as bad as the next person: I just do not see the less-fashionable plants. Be honest, when was the last time you went on hands and knees to study a moss or liverwort?

With the more garish flowering plants still reluctant to fully wake up, now would be a great time to explore some of the lesser know plant types.

Plants

The bryophytes, the mosses and liverworts, are mainly small plants with leaves and structures called rhizoids (rather than conventional roots). The visible plant (gametophyte) has only one set of chromosomes within each cell and this individual will produce sex cells that fuse to form the next generation – now with two sets of chromosomes. This new stage of the life cycle, called a sporophyte, asexually releases spores that give rise to a new gametophyte plant.

Because they have few water-retaining features, and sex cells that require water to allow fertilization, they are restricted to wet environments. They have little in the way of a water transport system – so are found in damp meadows, a base of a tree trunk or on wet walls.

The ferns (also the similar horsetails and club mosses) have a visible sporophyte and miniscule gametophyte. You should be able, in season, to see the spore producing bodies located below the fern frond (in most types). These are plants better adapted to life on dry land, having a vascular (transport) system for water and soluble foods.

More recently evolved are the gymnosperms, or conifers. The plant you see is a sporophyte. Gymno = naked [Yes, gymnasts used to perform naked!], sperm = seeds. Their seeds are not contained within an ovary – so are ‘naked’. When the conifer cones open the seeds are usually on the surface of the cone scales, so are ‘naked’. [See angiosperms for life cycle.]

The most recently evolved group of plants are the angiosperms, the flowering plants whose seeds are wrapped up inside an ovary i.e. non-naked. It is generally these angiosperms that dominate the land today with over 300 000 species, some ten times the number of gymnosperms.

Plant life cycle. N.B. Diploid = 2 Chromosome sets = Sporophyte and (7 & 9) are the small spores (pollen grains); (6) = large spore. (9) germinated to give the gametophyte (Haploid – one chromosome set), (11) the pollen tube with one sex cell and two others to make endosperm. (6) female / large spore germinates in situ to produce (10) containing an egg cell and an endosperm cell + others. (2) is seed formed from fertilized and developed sex cells + endosperm.

Plant life cycle. N.B. Diploid = 2 Chromosome sets = Sporophyte and (7 & 9) are the small spores (pollen grains); (6) = large spore. (9) germinated to give the gametophyte (Haploid – one chromosome set), (11) the pollen tube with one sex cell and two others to make endosperm. (6) female / large spore germinates in situ to produce (10) containing an egg cell and an endosperm cell + others. (2) is seed formed from fertilized and developed sex cells + endosperm.

The seeds, containing young root, stem, leaves and sometimes an extra food supply, the endosperm, are the result of fused sex cells. So seeds are distinct from spores, which are merely a package of cells.

The plant one sees is, in fact, a sporophyte – for the flower’s anther produces small numerous spores (pollen) and the female parts a few large spores. Each of these types of spores can germinate to generate a gametophyte – the pollen grows, on the stigma, to form a pollen tube, the female spores germinate in situ to make the ovule containing one egg cell (and several other cell types too). The pollen tube contains normally three cells, one of which will fuse with the egg cell to eventually give us the seed.

But it gets worse! A second pair of pollen tube cells will fuse with a single cell in the ovule to produce a cell with three sets of chromosomes – this may, or may not, develop; but if it does develop it forms a short-term food store (the endosperm) inside the seed’s coat. This endosperm is the flesh of a coconut or the flour inside a grain of wheat or barley. The wheat germ is the young potential plant with immature root, leave etc.

Finally, there are two different types of flowering plants: some have two young leaves (cotyledons) in their seeds, others only one. The dicotyledonous plants and the monocotyledonous plants – always called monocots and dicots. The monocots have parallel leaf veins (grasses, orchids); the dicots netted leaf veins (oak leaves, dandelion). There are subtle differences in the growth (see below) and their chemistry – hence the chance to develop ‘selective herbicides’.

Because the pollen tube of angiosperms is nourished and grows inside the stigma and style, to fertilize the egg cell, it is much less affected by the need for liquid water. The angiosperms are better adapted to life on dry land.

Plant type  Plant you ‘see’ Plant you ‘see’ Small stage
Mosses Gametophyte* Sporophyte
Ferns Sporophyte Gametophyte*~
Conifers Sporophyte # Gametophyte*@
Flowering plants Sporophyte# Gametophyte*@

*One set of chromosomes only, others have two sets.
~ Looks like a small liverwort
# Pollen is a spore
@ Formed from a germinated spore = pollen tube or ovule.

Ecology of grasses (monocots) and dicots

Generally the growing point of grass-like leaves is at the base of the plant, from a very truncated stem. Dicots leaves often develop and grow higher up, on a longer stem. With a grazing ecological system grasses will still be able to elongate (grow) their leaves despite being nibbled; dicots will have had their growth points eaten away and will be severely inhibited.

Of course, there are lots of exceptions – dicots, like clover, that can ground hug, but as a general ‘rule’ it works well enough.
Grazing a field will still allow grasses to grow, but invading trees and shrubs will be killed. Grazing stops succession and is a powerful conservation tool.

David is an ex-lecturer in Environmental / Biological Sciences.
He has written for most of the UK gardening magazines, including the RHS.
Forest Edge’s garden has been widely covered in magazines and has been featured in a BBC’s Gardeners’ World special.
He also maintains a blog at https://nwhwildlife.org/