h9. A GUIDE TO T H E M O R E C O M M O N F R E S H W A T E R P L A N T S OF T H E A U C K L A N D P R O V I N C E by Lois C. Armiger. This article is intended simply as an introduction to the fresh water plants most frequently encountered in Auckland, and has been designed especially for those who may wish to study them ecologically. The list of species is based largely on a knowledge of the vegetation in the Western Springs area. Most of them, and many more, have already been dealt with by Miss Ruth Mason in her post-primary school bulletin "Water Plants", which includes excellent diagrams of all types described. I am indebted to Dr. R. C. Cooper of the Auckland Institute and Museum for allowing the sketch of Jussiaea diffusa to be made from herbarium specimens in his care. Salvinia natans and Lagarosiphon major were drawn from fresh material. A l l figures are approximately half natural size. The plants are here divided into three groups according to whether they are (A) floating, (B) attached to the substratum and completely submerged, or (C) attached and at least partially emergent. A. F L O A T I N G (1) The Duckweeds These are actually monocotyledons, but have become so modified for the aquatic environment that they are difficult to recognise as such. They form more or less continuous sheets on the surfaces of ponds and other still water bodies, and are a characteristic light, very bright green colour. The individual plants consist of small, flattened stems, or fronds, having a leaf-like appearance; true leaves are lacking. Fine roots spring from the under surfaces of the fronds and depend into the water. The minute reproductive organs arise in little pockets in the skin, but are comparatively rare: propogation is predominantly vegetative by thebudding off of daughter fronds which eventually become detached. Two species occur in the Western Springs area: - Lemna minor, which has one root only to each frond, and is green all over; this is a cosmopolitan species, common throughout the country, and it is not certain to what extent it may be introduced. (2) The Water Ferns Like the duckweeds, water ferns, especially the smaller ones, may also form rather extensive sheets in quiet waters, and have little obvious resemblance to other members of their class. In the vicinity of Auckland city two species may be found - a tiny native, Azolla rubra, and a much larger, introduced plant, Salvinia natans. Each frond of Azolla comprises a short, much-branched stem densely covered with diminutive, overlapping (imbricate) leaves. Its colour is a soft, misty green which becomes
SURFACE VIEW L A T E R A L V I E W SALVINIA NATANS
51. tinged with red, and eventually completely reddened, as the plant advances in age. As in the duckweeds, fine roots depend from the undersurface of the frond; here appear, too, the reproductive bodies, called sporocarps. Salvinia consists of an elongated, rounded stem bearing at intervals (i. e. at each node) a pair of relatively large, floating leaves and a cluster of root-like structures, which actually represent a dissected submerged leaf. The floating leaves are petioled, rather brittle with slightly wavy, (undulate) margins and a dense covering of huge, terminally looped, white hairs on their upper surfaces; they vary in form from more or less cordate, (heart-shaped) to distinctly bilobed and folded along the mid-line. Small brown scales are scattered over the stem, petioles and "roots". The reproductive bodies grow out in small groups from the bases of the latter. This species has recently become a great menace in the Western Springs Lake; it probably "escaped" thither from garden fish-ponds, in which it is often cultivated. B. A T T A C H E D A N D C O M P L E T E L Y S U B M E R G E D (1) Algae Two types of macroscopic green algae commonly occur in fresh water: - (a) The charophytes, species of Chara and Nitella, which are made up of whorls of lateral appendages about a longitudinal axis. The component cells are extremely long, transparent cylinders, and the plants have conspicuous orange-red or yellow reproductive bodies. Excluding differences in these reproductive organs, the two genera are somewhat difficult to separate: Chara. however, usually tends to be larger and coarser than Nitella, and frequently has a corticated structure - i. e. the axis consists of a large central cell surrounded by smaller ones. (b) The filamentous green algae, such as Spirogyra, which form rather slimy, shapeless masses of fairly dark coloured material on rocks and in pools. They consist of single, cylindrical cells joined end to end in long filaments. The genera most likely to be met with nearly all have some distinctive cell feature: Spirogyra, as is well-known, has very characteristic large, spiral chloroplasts; in Zygnema the chloroplasts are stellate (star shaped); in Cladophora they are generally reticulate (in the form of a network); Oedogonium produces, by its peculiar method of cell division, a series of "apical caps" at the anterior extremities of the cells; Rhizoclonium typically gives rise to small, colourless rhizoids at the cell junctions. (2) Mosses The commonest aquatic species of moss are Fissidens rigidulus and Drepanocladus fluitans, though various other members of these two genera may also colonise more or less watery habitats. Fissidens, which is plentiful at Western Springs, can be entirely submerged when growing on stones in streams and creeks. It is always a close, dark green mat. Microscopic examination of the leaves reveals that they have (1) stout, multilayered borders, except at the tip, (2) a nerve (midrib) extending throughout their whole length and (3) dense, dark cells
52. Drepanocladus, on the other hand, usually forms tufts or patches in swampy places and quiet waters, and has a golden-brown, yellow-brown or light green colour. The leaf margins are flat, not thickened, and slightly toothed at the base and/or the apex; the nerve reaches to the middle of the leaf or somewhat higher, but not right to the tip, and the cells at the basal angles of the leaf are enlarged to form clear lobes (auricle s). Both mosses are fairly widely distributed throughout New Zealand. They are native, but occur also in other countries, Drepanocladus in Northern and Southern Hemispheres, Fissidens only in the South. (3) The Oxygen Weeds Three species of oxygen weed have been introduced into New Zealand - Anacharis (Elodea) canadensis, Egeria densa, and Lagarosiphon major Anacharis almost completely covers the lake bottom at Western Springs. It is attached to the substratum by numerous well-developed roots, and the stem stretches upwards, through the water, often attaining a considerable length; the narrow, thin, translucent leaves are borne mostly in whorls of three, but become crowded towards the apex. The inconspicuous flowers are extremely simple in structure and are the only sure means of recognising the plant as a monocotyledon; they float out from the main axis on unusually long, thread-like peduncles. Also present in the Western Springs Lake, but much less plentiful, is Egeria. It is very similar to Anacharis, but has considerably larger leaves, borne in whorls of at least four. Lagarosiphon, the third member of this family to be found in the district, but is particularly common around Rotorua, has stiff, strongly recurved leaves, arranged more or less spirally. In the Western Springs area it seems to be restricted almost entirely to the streams. (4) The Water Milfoils. These are all species of the genus Myriophyllum, and may form fairly dense growths, usually in still waters - ponds, lakes, lagoons, swamps, and slow-flowing streams. They are characterised by whorls of very finely divided (pinnatifid or pinnatisect) leaves, the segments of which may even be capillary (hair like). Only the uppermost, youngest leaves are undivided, except in the two rarer, smaller species which have all their leaves entire. The flowers which enable the milfoils to be identified as dicotyledons are quite minute, and are borne singly in the leaf axils. Probably the most common species, and certainly the most widespread in the Western Springs area, is M. elatinoides. The pinnatisect leaves of this plant change, usually quite abruptly, to ovate-oblong, sessile, upper leaves, frequently reddishtinged and crowded into a bud; the very uppermost are entire, while the intermediate ones have serrated margins. Sometimes, however, these upper leaves are completely lacking. The stems are normally pale, contrasting sharply with the dark green of the leave s
LAGAROSIPHON MAJOR
54. M. propinguum exhibits a great diversity of leaf form - a graduation from pinnatisect through to entire, linear leaves. Generally only pinnatifid (having pairs of lobes, or pinnules) and linear leaves are present; they are I - lj cm. long and very narrow. M. robustum is extremely large and stout, and never has any entire leaves at all. It is a much more localised plant than the other two specimens. The myriophyllums are all native. Their distinctive leaf form appears to be a means of increasing the absorbing surface of the leaf, possibly in adaptation to the aquatic habitat. (5) The Pondweeds - in part. The so-called pondweeds are members of the genus Potamogeton, two species of which occur as submerged plants, while the remaining three are partly submerged and partly emergent. The latter are more widespread than the former, which have leaves of one type only. A l l are native, and are found in ponds, lakes, and moderately slow rivers and streams They are easily recognised as monocotyledons by the parallel primary venation of their alternate leaves. The flowers are small, green, and aggregated into a terminal spike. P. ochreatus has linear, membranous, strap-shaped leaves with blunt tips and 3-5 major nerves. P. pectinatus has extremely narrow, filiform or threadlike leaves, drawn out into five points. The upper ones are grooved, the lower ones flatter with 1-3 nerves. This species is localised in distribution but abundant in parts of the Waikato area. C. R O O T E D A N D E M E R G E N T (1) Potamogeton - in part The most widely distributed of the native pondweeds, and certainly the most prevalent of those which are grouped under this heading, is JP. cheesemanii. Its upper, emergent leaves have long petioles, are elliptical to oblong in shape, rounded at both base and apex, thick and leathery in texture. The lower, submerged leaves are but shortly petioled, about twice as long as the floating ones, oblong to lanceolate to linear in shape, thin, membranous and translucent, often with wavy margins. (2) Cape Pond weed - Aponogeton distachyus. This monocotyledon has been introduced from South Africa and is frequently found in ponds and slow-flowing streams. The submerged leaves are tufted and linear, the floating ones have long petioles and are linear oblong. A characteristic two-branched spike of white flowers is produced: from this the specific name of the plant is derived. The leaf petioles and flower peduncles, as also the stems of the oxygen weeds and water milfoils, contain very well developed systems of air spaces (aerenchyma) - a feature typical of water plants in general.
Plants of the remaining five sections to be dealt with in this group can all be recognised as dicotyledons by the net venation of their leaves; the only possible exception i s : - (3) The Water starworts - Callitriche spp. in which this feature is somewhat poorly developed, but which have, in any case, opposite leaves. The most common species is C_. stagnalis, abundant in still waters and on wet mud. The leaves may vary considerably in size according to the nature of the substratum on which the plant grows. The lower, submerged ones are usually rather long and narrow, grading into the spoon-shaped (spathulate) and obovate upper ones, which form characteristic floating rosettes of a bright, pale green colour, similar to that of the duckweeds. The minute flowers and fruit are borne in the axils of the leaves. Two other species which may occur in the Auckland region, though much less commonly are: - C. muelleri, which has rhomboidal (diamond-shaped) leaves. C. petrei, with spathulate leaves like those of C_. stagnalis, but substantially smaller. (4) Water Cress - Nasturtium officinale This introduced plant is widely distributed in streams, along stream banks and in other wet places. It is easily distinguishable by its pinnate, fairly dark green leaves, white flowers with four petals in the form of a cross, and long pods typical of the family Cruciferae. (5) Polygonum spp. Two very similar introduced species of this genus are common in watery habitats such as the edges of ponds and streams. Both are characterised by typically reddish stems with alternate, rather long narrow, pointed leaves, which may also be tinged with red, and tubular structures termed ochreae ensheathing the stem at the nodes The small pinkish flowers form stalked inflorescences arising in the axils of the leaves. P. hydropiper (Smartweed) has a rather burning, peppery taste when chewed, the ochreae are short, the leaves have roughish margins, and the inflorescences are long, lax, and drooping. P. persicaria (Lady's Thumb) has, on the other hand, no peppery taste, longer ochreae which closely hug the stem, smoother leaf margins, and compact, almost erect inflorescences. (6) Water Purslane - Ludwigia polustris Yet another introduced species found in swampy ground, ponds and streams. It is usually tinged with dark red, has more or less quadrangular (four-angled) stems, opposite, oval to ovate - lanceolate leaves, and small flowers, much the same colour as the stem and sessile in the axils of the leaves: they give rise to rather square shaped fruits. Roots are formed at the nodes of the submerged parts of the stems.
JUSSIAEA DIFFUSA
m\ 57. (7) Primrose Willow - Jussiaea diffusa This plant is rather similar to the previous one in habit and habitat, and is also introduced. The stem is terete (cylindrical), the leaves alternate, and ovate to obovate - lanceolate in shape; the yellow flowers, on slender stalks (penducles) produce a slightly tapered cylindrical capsule. (8) Sedges and Rushes Many sedges and rushes may grow around the margins of water bodies and in swampy ground The rushes are primarily species of Juncus: they have terete stems, leaves which are identical with the stem, or else flattened and grass-like, and are smooth all over; the flowers have a perianth of undifferentiated members (tepals), usually arranged in two whorls of three, and the fruit is a dry, dehiscent capsule containing many minute seeds The sedges belong to a number of different genera: their stems are often triangular or even quadrangular, and sometimes obviously jointed: the leaves are narrow, grass-like and arranged in basal tufts, or in some cases lacking or reduced to sheathing scales; many of the species are scabrid (rough) as, for example those which are commonly termed "cutty-grasses"; the perianth of the flower is reduced to scales, bristles, or hairs, and may often be absent altogether, while the fruit is nutlike and does not dehisce (burst open) when ripe. (9) Typha Also frequently met with is Typhya muelleri ( T_. angustifolia) the Raupo or native bulrush; the elongated, compact, dark brown seed head on a tall, stout stalk, and long, greyish-green, sword-like leaves render it quite unmistakeable