Tuatara: Volume 5, Issue 1, January 1953
A Key to the New Zealand Lycopods
A Key to the New Zealand Lycopods
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.
|(1)||Spore-producing organs with two or three externally visible compartments||Psilopsida *|
|Spore-producing organs with one compartment||— 2page 7|
|(2)||Branches in whorls radiating at intervals up the stem||Sphenopsida† (Horsetails)|
|Branches not in whorls||— 3|
|(3)||Leaves generally large, much divided, with spore-producing organs occurring in various positions on their undersides||Filicopsida (Ferns)|
|Leaves small, undivided, with spore-producing organs typically crowded into terminal cone-like structures known as fertile spikes||Lycopsida (Lycopods)|
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.
|1||Leaves and fertile spike arising directly from a tuber. Plant 1-2½ in. high. (Fig. 7)||Phylloglossum Drummondi|
|Leaves and fertile spike arising from normal stems||— 2|
|2||Two types of leaf on each adult, sterile branchlet. The largest leaves in 2 rows lying in one plane||— 3|
|One type of leaf on each sterile branchlet. Leaves arranged in many vertical rows||— 4|
Legend to Figures
(These figures are not drawn to the same scale) Fig. 1: L. densum (x 3½). Fig. 2: L. ramulosum (x 1½). Fig. 3: L. laterale (nat. size). Fig. 4: L. scariosum, (a) sterile branchlet (x 3½), (b) fertile spike. (x2). Fig. 5: L. volubile, (a) sterile branchlet (x 3½), (b) fertile spike. (x 2). Fig. 6: L. cernuum (x 2½). Fig. 7: Phylloglossum drummondi (x 4). Fig. 8: L. selago (nat. size).
|3||Sterile branches trailing, fan-like, with the smaller scale leaves on both upper and lower sides. Branches bearing fertile spikes forking repeatedly. Tips of fertile leaves not prominent. (Fig. 5)||L. Volubile|
|Sterile branches erect, much divided, with the smaller scale leaves on the under side only. Branches bearing fertile spikes divided sparingly. Tips of fertile leaves prominent, long, directed outwards. (Fig. 4)||L. Scariosum|
|4||Leaves bearing sporangia unmodified foliage leaves. Spore-producing organs not aggregated into spikes. (Fig. 8)||L. Selago|
|Leaves bearing sporangia differing from foliage leaves in size and shape. Spore-producing organs aggregated into more or less distinct spikes||— 5|
|5||Fertile spikes lateral on erect branches. Spikes brown or reddish-brown. Swamp habitats. (Fig. 3)||L. Laterale|
|Fertile spikes terminal||— 6|
|6||Fertile spikes arising among unmodified sterile leaves||— 7|
|Intermediate zone between sterile and fertile leaves||— 9|
|7||Fertile spikes terminal on short lateral branches (sometimes terminating the main branches). Brown or reddish-brown. Stems prostrate branching by equal dichotomies. Swamp habitats. (Fig. 2)||L. Ramulosum|
|Fertile spikes terminal on ultimate branches||— 8|
|8||Leaves of a common form, short, closely appressed to the stems. Stems densely branched. Fertile spikes numerous, ½-1 in. long. (Fig. 1)||L. Densum|
|Leaves longer, narrow, directed outwards. Stems much divided. Fertile spikes numerous. ¼-½ in. long. (Fig. 6)||L. Cernuum|
|9||Sterile leaves ¼-¼ mm. broad||— 10|
|Sterile leaves 1-2 mm. broad||— 11|
|10||Main stem creeping, producing copious roots. Foliage dark-green. Fertile spikes long, 1-3 in. or more. Yellow-green. (Swamp near Kaitaia, only known locality.) (Fig. 10)||L. Drummondi|
|Main stem underground. Primary branches erect, much branched. Fertile spikes long, ¾-2 in. or more. (Fig. 12)||L. Fastigiatum|
|11||Fertile spikes usually unbranched. Transition from sterile leaves to fertile leaves, steep. Branches stout, erect. (Fig. 11)||L. Varium|
|Fertile spikes long, slender, dichotomously forked. Branches commonly pendulous||— 12|
|12||Terminal fertile leaves usually no longer, or only slightly longer, than the sporangia. Fertile spikes repeatedly forked. Branches stout, 1-5 ft. long. (Fig. 9)||L. Billardieri|
|Terminal fertile leaves distinctly longer than the sporangia. Fertile spikes sparingly forked. Branches slender, 6-12 in. long. (Fig. 13)||L. Billardieri var. Gracile|
(These figures are not drawn to the same scale) Fig. 9: L. billardieri (nat. size). Fig. 10: L. drummondi (x 1½), (a) fertile spike, (b) sterile branch. Fig. 11: L. varium (x ⅔). Fig. 12: L. fastigiatum, (a) fertile spike (x 1½), (b) sterile branch (x 2). Fig. 13: L. billardieri var. gracile, fertile spike (x 1½).
Smith, G. M. (1938).—Cryptogamic Botany. Vol. 2. McGraw-Hill.
Holloway, J. E. (1920).—Studies in the New Zealand species of Lycopodium. Part IV. Trans. N.Z. Inst., Vol. 52, pp. 193-239.
Holloway, J. E. (1936).—‘Links in the New Zealand Flora with the Remote Past.’ Cawthron Lecture.
* A group of primitive rootless plants with only two living genera—Psilotum and Tmesipteris. Both occur in New Zealand. (See ‘Living Fossils of the Plant Kingdom’, Vol. IV. No. 2)
† Represented by the remnant genus Equisetum of which there is no native species.