Flora of New Zealand Series

Raceme of few to many fls; floral bracts membr. to foliaceous. Per. glab.; dorsal sepal uppermost, concave, ± arched over column; lateral sepals and petals narrower. Labellum shortly if at all clawed, undivided and with entire margins and 2 basal calli. Column semi-terete, incurved above; anther standing at least partly above stigma, pollinia mealy; stigma prominent; rostellum us. 2-lobed. Plants terrestrial, glab.; tubers small, globose, the new ones often remote from the parent plant. Green lf solitary, petiolate on non-flowering stems, sessile on flowering stem; lamina short and broad, length rarely 2 × width. Some 20 spp. described, most of them from New Caledonia; of 5 Australian spp. 3 are represented in N.Z. Also recently recorded from Solomon Is and New Guinea.

Cheeseman (T.N.Z.I. 7, 1875, 349-352) described fertilisation of the fls of 2 spp.

The genus Acianthus was based on 3 spp. all possessing the following group of characters: sepals aristate (whence presumably the generic name) and longer than the petals; column unwinged; pollinia in each loculus of the anther 4, or 2 bipartite. Schlechter (Engl. Bot. Jb. 39, 1906, 39-42), in combining Cyrtostylis with Acianthus, brought in plants which showed none of these characters. The broader concept of the genus seems to have been generally accepted and this leaves little justification for maintaining Townsonia Cheesem., 1906. The column of A. reniformis is winged throughout, though less widely than in A. viridis, and neither of these spp. has 4 distinct pollen masses in each loculus of the anther. The petiolate lf near or some distance from the base of the flowering stem is especially mentioned as a generic character of Townsonia by Schlechter (Fedde Repert. Spec. nov. Regn. veg. 9, 1911, 249) but similar petiolate lvs, each arising also in connection with a tuber, occur in non-flowering plants of both A. fornicatus and A. reniformis. The difference lies in the fact that in A. viridis the rhizome (or root?) is fleshy and long-lived, often including at one time some branches with flowering stems and some with petiolate lvs; in the other two spp. the link between two tubers is slender and short-lived, being broken before either produces its flowering stem or petiolate lf as the case may be. Similar differences occur within the genus Corybas.

Fig. 21. ACIANTHUS Lettering as in fig. 20, p. 103; Tu = tuber. © All rights reserved. [Image: 4X2D]