Art. XLVIII.—On Zannichellia and Lepilæna in New Zealand.
[Read before the Wellington Philosophical Society, 26th February, 1896.]
Zannichellia palustris, L., was first discovered in New Zealand by Colenso; it was included by Sir Joseph Hooker in his original “Flora of New Zealand,” published in 1853, and sub-sequently in the “Handbook of the New Zealand Flora,” Colenso's habitat on the East Cape being for many years the only local station recorded for the plant. On its discovery in the Waikato in 1870, the learned Baron von Mueller suggested the strong probability of its belonging to the Australian genus Lepilæna, the principal species of which were formerly confused with Zannichellia, and, at his request, some of the Waikato specimens were submitted for his examination, when they were kindly identified by him as Lepilæna preissii, F. Mueller. The plant exhibited a very close resemblance indeed to a European form of Zannichellia, with the achenes on long slender pedicels, the similarity extending even to the form of the ripe fruits. This identification, however, led local botanists to assume, somewhat hastily, that, as in Australia so in New Zealand, all plants hitherto indentified as Zannichellia must be referred to Lepilæna; and the older genus was completely neglected until three or four years ago, when Mr. Petrie detected Zannichellia palustris in Otago, and I had the pleasure of collecting it in flower and fruit in the Makararoa Stream, Hawke's Bay, a locality which affords strong support to the accuracy of Sir Joseph Hooker's determination of Colenso's original specimens. As it is probable that both Zannichellia and Lepilæna are of more frequent occurrence than has hitherto been supposed, it seems desirable that attention should be drawn to the chief characters by which the members of these closely-allied genera may be most readily identified. Both are inconspicuous submerged aquatics, with capillary stems and leaves, and axillary apetarlous flowers; the leaves in both are from ½in. to upwards of lin. in length.
Zannichellia is monæcious. The male flower is enclosed in a membranous bract, and consists of a single sagittate anther, with the filament at first short and stout, but ultimately much elongated. The female flower is also protected by a membranous bract, and consists of from four to six carpels sessile or shortly stalked, with short styles and capitate stigmas. The
fruits are curved achenes, tipped with slender styles, and arranged in fascicles of from three to six. In European specimens the dorsal margin of the achenes is more or less crenulate or rarely spined, but this character is not strongly marked in the New Zealand specimens. A plant with the achenes more than three in a fascicle may safely be referred to Zannichellia; rarely, owing to suppression, the achenes may be reduced to three or two, when the genus must be determined by the monœcious or diœcious habit. The cotyledon is twice folded in Zannichellia.
The only habitats in which Z. palustris has at present been observed in the colony are Mercer, Rangiriri, and other places in the Lower Waikato; Waikaremoana, Whangape, and Waihi Lakes : T. Kirk. East Cape district: W. Colenso (Handbook). Makararoa Stream, Hawke's Bay : T. K. Waikouaiti Lagoon, Otago : D. Petrie !
The only species observed in the colony is Z. palustris, which varies considerably in the shape of the fruits and the length of the styles. The Rangiriri plant has rather turgid, almost sessile carpels, which closely approach the form known in Europe as Z. polycarpa, but the styles are longer; usually the carpels are carried on short pedicels.
Lepilæna is characterized by diœcious flowers, the males solitary in the axils of the leaves, and consisting of three, or rarely two, sessile anthers, each seated in a minute perianth at the apex of a very short peduncle, the whole invested by the dilated and sheathing bases of two opposite leaves. The anthers are two - celled, the cells opening by slits on the outer face, and are monadelphous, cohering dorsally, so that they resemble a six-celled anther. The pollen is produced in great profusion, and appears to be discharged in the water before the full development of the female flowers; but further observations are required on this point. The female flower consists of three free carpels, which may be sessile or shortly stipitate : they spring from the apex of a very short peduncle with minute teeth. The perianth consists of three membranous bracts, and is closely invested by the dilated and scarious bases of the floral leaves. The fruits are three in number, rarely two; sessile, or on rather long pedicels, usually with long slender styles : the dorsal margin is quite entire.
L. preissii, F. Mueller, has only been found in the Waikato River near Churchill, where it occurred in considerable quantity and in great luxuriance, some of the slender stems exceeding 18in. in length. As it was late in the season (24th April) when collected, only fruiting specimens were obtained, with two or three imperfect female flowers. The male flowers have not been observed.
In 1881 I discovered another species in the Canterbury District, and recorded it under the name of L. biloculata in the report of the School of Agriculture, Lincoln, 1884 (second term). As will be seen from the appended description, it differs in several important particulars from any other species.
Lepilæna bilocularis, T. Kirk, in Report of Sch. of Agric., Lincoln, 1884.
Stems much branched, capillary, 3in.— 12in. long. Leaves flat, slightly broader than the stem, linear, one-nerved, obtuse. Male flowers enclosed in the dilated sheathing-bases of two opposite floral leaves. Anther solitary, sessile, on a short three-toothed peduncle, broad, connective produced, acute, the anther dehiscing from the apex. Female flower : perianth of three lanceolate membranous bracts at the apex of a short peduncle, carpels three, sessile, styles equalling or exceeding the perianth, stigmas dilated; reflexed, deeply fimbriate, exserted. Achenes three, rarely two; dorsal margin entire, style more than half the length of the achene, usually straight.
South Island.—Canterbury—drains and streams running into the Selwyn. In a small stream near the outlet of Lake Ellesmere : T. Kirk. Otago—Waihola Lake : D. Petrie !
The leaf-bases enclosing the male flowers are developed to a remarkable extent, the upper free portion on each side of the leaf presenting a stipular appearance, and appears to be composed of two (or perhaps three) membranous bracts adnate with the bases of the floral leaves. The leaf-bases investing the female flowers are much smaller.
The plant exhibits a departure from the usual characters of the genus—(1) In the large solitary anther which dehisces from the apex downwards, the cells diverging laterally; (2) in the produced connective; (3) in the reflexed and almost laciniate stigmas, which are very conspicuous.
Submerged aquatic plants have received little attention from New Zealand botanists, although it can hardly be doubted that other species will reward careful search.