At the present time the Lycopods play a comparatively insignificant role in world vegetation, both numerically and in individual size, and for this reason they can be easily overlooked by the amateur. However, many millions of years ago, during the Carboniferous period, the ancestors of the present Lycopods and those of the related ‘Horsetails’ were among the few groups which dominated the world's plant population. The all-important flowering plants of to-day did not exist, the ancestors of the cone-bearing plants occupied a minor position similar to that of the Lycopods to-day, and even the ferns, which are now the commonest spore-producing plants, played a secondary role.

The most notable Lycopod of this age was Lepidodendron, a genus for which over 100 species have been described. The details of some of these species are known almost as well as those of many living plants, even though they have been extinct for almost 200,000,000 years. Fossilised roots, stems, leaves and fertile spikes have been closely studied and carefully correlated with one another to reveal the rather surprising fact that many of these ancient forms were large trees, attaining a height of as much as 120 feet in some cases. The tree Lycopods and tree Horsetails formed vast swamp forests, and together they played a major part in the formation of the world's most important coal fields. Insofar as modern society depends upon the major coal areas, we are that much indebted to the ancestors of seemingly insignificant groups of plants.

The Lycopods are collectively known as the Lycopsida, which is one of four classes comprising the division Pteridophyta. This division can be defined as an intermediate group of land plants which reproduce by spores, not seeds, and in the short key which follows, an attempt is made to define the four classes mentioned.

To-day only 4 lycopod genera remain—Lycopodium, Phylloglossum, Selaginella and Isoetes and the species included within these are all comparatively small plants, revealing nothing, superficially, of their former greatness.

As might be expected with remnants of such an ancient group, their distribution tends to be world-wide. For instance, of the 11 species of Lycopodium native to New Zealand, 9 occur elsewhere in the world.

Phylloglossum is more restricted, being found in New Zealand and Australia only. The one existing species is an unusual little plant, which consists of a single fertile spike and a tuft of narrow leaves arising from a tuber-like stem. Each season a new tuber is formed, which produces a spike and new leaves in the following year.

Selaginella has many widespread species. It is a genus of rather slender-stemmed plants, none of which occur naturally in New Zealand, although there is one introduced species—S. kraussiana. This is a creeping, rather delicate, shade-loving plant which is found quite commonly in some localities.

The relationships of Isoetes are rather uncertain, although most authorities now place it among the Lycopods. This mainly aquatic genus is characterised by a short, corm-like stem from which arise many long, slender leaves. A spore-producing organ occurs at the base of each leaf. There are two species of this genus native to New Zealand, and both are submerged aquatics which are distinguished mainly by size. I. Kirkii is slender and up to 12 inches high, I. alpinus is stout and up to 18 inches high or more. It almost seems as if the aquatic habit of Isoetes has protected it from the struggle for survival on the land which resulted in the extinction of its relatives.

In common with most plants, the Lycopods exhibit two stages in their life cycle. The one is a comparatively small, tuberous, underground structure which produces male and female sex organs; the other, which comes into being as a result of sexual reproduction, is what we regard as page 8 the ‘plant’. The latter stage eventually produces spores, which give rise to the underground sexual stage again and so the cycle is completed. These spores possess quite intricate patterns of external sculpturing, which make them attractive objects for microscopic study.

The foregoing is a very general account of the Lycopods, but it is sufficient to show the wide scope for research on our New Zealand species. One New Zealander, the late Dr. J. E. Holloway, attained world recognition for his investigations of Lycopodium, Psilotum and Tmesipteris. He published many papers describing their external variability, their internal anatomy and the nature of their tuberous sexual stage which should certainly be read by any botanist interested in the group.

Key to the New Zealand Species

Users of this key should note that species determination may be difficult in some cases, owing to the tendency of Lycopodium species to vary considerably from habitat to habitat; e.g. L. varium is usually a stout terrestrial plant which, when it is occasionally pendulous, may be very similar to L. billardieri. L. billardieri itself is notoriously variable, normally having greatly reduced fertile leaves, but occasionally plants may be found where these parts are much nearer to foliage leaves in size.

Other difficulties are the juvenile stages of L. volubile and L. scariosum, which possess only one type of leaf set all round the stem, and the peculiar case of L. densum which exhibits three types of adult leaf, which are usually on different branches. Two are long and directed outwards, the third shorter and closely appressed to the stem. The latter type is the most diagnostic and, as all three generally occur in each locality, it can be safely used as a key character.

For detailed descriptions of the species dealt with in this paper, refer to Cheeseman's Manual of the New Zealand Flora.

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