Plant Divisions: Lycopodiophyta

Clubmoss Selaginella kraussiana

Clubmoss Selaginella kraussiana

Plants within the division Lycopodiophyta are small, green, leafy and have spores but no flowers. They are a little like mosses, and many contain the word ‘moss’ in their common names. However, Lycopodiophyta evolved later than plants in the Bryophyta division and have a fully formed vascular system, with phloem and xylem, they are the earliest vascular plants to have evolved. There are about 2,000 species in total, and although they are more numerous in the tropics, they grow throughout the world.

There are, broadly speaking, four different types of plant within the Lycopodiophyta Division: clubmosses, firmosses, spikemosses and quillworts. The following diagram shows how they fit together in the plant kingdom. (click to enlarge)

Lycopodiophyta Family Tree

Lycopodiophyta Family Tree

  • Class – all end with ‘opsida’
  • Order – all end with ‘ales’
  • Family – all end with ‘aceae’

Of the four families within the Lycopodiophyta Division, Lycopodiaceae, the clubmoss family, is the largest and most diverse, containing between 13 and 19 genera. The spikemoss (Selaginellaceae) and quillwort (Isoetaceae) families contain only one genus each, although within those genera are many species.

Note: Lycophyte is a general term for plants in the Lycopodiophyta Division.

What makes lycophytes different from other plants?

Leaves

Lycophytes are distinct from most other plants, by having microphylls, a primitive form of leaf. Microphylls are a few evolutionary steps on from the leaves of BAMs (Bryophyta, Anthocerophyta and Marchantiophytasee previous blog) which are mostly one cell thick and without specialization. Microphylls can be many cells thick, with special cells for the epidermis and vascular tissue. They are not necessarily small – extinct Lepidodendron had microphylls over a metre long – but they are simpler than normal leaves, which are called megaphylls. Whereas megaphylls have a complex network of veins, or a number of veins running from base to tip, microphylls have a single, unbranched vein.

Horsetails (a type of fern) also have microphylls, but from the fossil record it looks as if they evolved megaphylls and then reverted to microphylls later.

Reproduction

See previous blog Plant Divisions: Mosses, Liverworts and Hornworts for more information about gametophytes and sporophytes.

Like BAMs (Bryophyta, Anthocerophyta and Marchantiophyta), lycophytes have alternating generations. The sporophyte stage produces spores and these grow into the gametophyte stages which produce sperm and eggs which then fuse to form a new sporophyte. However, there are a few important differences.

One difference occurs only in spikemosses and quillworts. BAMs, clubmosses and firmosses are homosporous, which means that all spores produced look identical and only become apparently male or female when the spores become gametophytes. Spikemosses and quillworts  are heteropsorous, meaning they produce two types of spores that look very different: large megaspores (female) and small microspores (male).

Heterosporous Reproduction

Selaginella - Heterosporous Reproduction

Selaginella – Heterosporous Reproduction

A fertile cone grows out from the sporophyte (the sporophyte is the main body of the plant, the part that has leaves), from this grow sporangia that contain spores, some the male microspores, others the large female megaspores.  When these spores are released they become separate, tiny plants, the gametophytes. The male gametophyte releases sperm, the female contains eggs. The sperm find and fertilise the egg by swimming to it after it has rained. The new sporophyte then grows out of the female gametophyte, putting down roots and growing leaves, becoming a whole new plant.

Other Differences in Reproduction

  • The female gametophyte generation has rhizoids, the more primitive form of root, while the sporophyte generation has roots
  • The sporophyte generation is the larger, longer lasting stage; in BAMs it is the gametophyte stage
  • Unlike BAMs, the gametophyte generation is completely removed from the sporophyte generation. In some lycophyte species gametophytes grow on the surface of the ground, others grow in water.

Different Types of Lycophytes

Spikemoss, Quillwort, Clubmoss, Firmoss

Spikemoss, Quillwort, Clubmoss, Firmoss

Pictures taken from here:

Clubmoss

Some clubmoss  shapes

Some clubmoss shapes

Clubmosses are in the Lycopodiaceae family, they have needle-like or scale-like leaves, a few of the different leaf shapes can be seen above. They are the most varied within the Lycopodiophyta Division, descibed as having between 13 and 19 genera and somewhere between 400 and a thousand species. Although most clubmosses are only a few centimetres high, and green, there are a few exceptions, for example Lycopodium deuterodensum, that grows in Australasia, can reach a metre high and Lycopodium fastigiatum, native to New Zealand, is orange in colour.

Clubmosses usually have a creeping or epiphytic habit (grow on other plants, or sometimes inanimate objects, high up). Most grow in tropical mountains, but they are found throughout the world, including in the UK. Clubmosses are homosporous and although their reproductive lifecycle is similar to the one shown above, the male and female spores are the same size and shape.

Firmoss

Firmoss

Firmoss

Firmosses are in the Huperziaceae family. They are mostly epiphytic and grow throughout the world. There are over 400 hundred different species of firmoss, although their appearance does not change much from one to another. They are more upright than clubmosses tend to grow in clusters, looking like a small fir tree forest. They are also homosporous.

Spikemoss

Some spikemoss shapes

Some spikemoss shapes

Spikemosses are contained in one genus, Selaginella, but there are still a number of different leaf shapes within the 700 or so species. In the US it is sometimes grown as a houseplant or as ground cover. It is heterosporous having both micro and megaspores.

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Spikemoss diagram

Spikemoss diagram

Quillwort

Quillwort

Quillwort

Quillworts are in the order Isoetales, which, like the spikemoss order, has only one family and genus, but about 150 species. Most are aquatic or semi-aquatic plants. Some species have been found off the coast of Scotland. The leaves are narrow and grasslike and it is difficult to distinguish from grass without a microscope. It is heterosporous.

A website tracking lycophytes in the UK is here http://www.ferns.rogergolding.co.uk/ferngenus/isoetes/echinospora.html

Extinct Species

Sigillaria and Lepidodendron Trees

Sigillaria and Lepidodendron Trees

Originally Lycopodiophyta contained three other orders: Lepidodendrales, Pleuromeiales in the Isoetopsida class and Drepanophycales in the Lycopodiopsida class. Plants in these three orders grew metres high, some up to 30m high, and formed forests in the Carboniferous Period 300-350mya. Tree ferns and early conifers also grew in Carboniferous forests. Coal formed from the decaying plant matter in these forests.

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