Flora of New Zealand Series

Type species: L. filiformis (G.Forst.) Trin.

Tufted, sometimes short-lived perennials, or annuals; branching intra- or extravaginal. Leaf-sheath rounded. Ligule membranous. Leaf-blade flat, or folded with inrolled margins. Culm erect or geniculately ascending, fragile at maturity; nodes glabrous. Inflorescence a lax, often delicately branched panicle; at maturity completely detached from the plant together with a fragment of the uppermost culm internode, or, in annual plants, soon withering and persisting. Spikelets small, 1- or occasionally 2-flowered, laterally compressed; disarticulation above glumes; rachilla often prolonged, tipped with soft hairs and almost equalling the palea, or prolongation minute and glabrous. Glumes ± equal and equalling the spikelet, ovate-elliptic to lanceolate, acute, membranous, often shining, 1-(3)-nerved, lateral nerves, if present, very short; keel ± scabrid. Lemma <, and thinner in texture than glumes, rarely (L. tenuis) ≈ glumes and firmer, elliptic-oblong, truncate, rounded, (3)-5-nerved, often denticulate and with lateral nerves minutely excurrent, usually with dense or sparse, soft, fine hairs, or sometimes glabrous, rarely (L. tenuis) finely scabrid; awn, finely scabrid, geniculate or straight, ± middorsal or very short and subapical, rarely 0. Palea from ½ to ≈ lemma, hyaline, keels 2, usually faint, close together at centre. Callus minute, blunt, with short, soft hairs, to ½ or rarely to ⅔ length of lemma, sometimes 0. Lodicules 2, linear to lanceolate, hyaline, glabrous. Stamens 3; anthers not penicillate. Ovary glabrous; styles distinct, free to base, short; stigmas 2, plumose. Caryopsis fusiform; embryo small; endosperm doughy or dry. Chasmogamous (N.Z. spp.). Fig. 9.

c. 20 spp. of Australasia, New Guinea and Easter Id, with the type sp. occurring throughout the range of the genus and naturalised in South America, South Africa and Malesia. Endemic spp. 10, indigenous spp. 2, 1 shared with Australia, 1 shared with Australia, New Guinea and Easter Id.

Lachnagrostis is generally included within Agrostis, e.g., Clayton and Renvoize (1986 op. cit. p. 134). However, in Lachnagrostis the whole inflorescence together with a fragment of the uppermost culm internode becomes detached at maturity and blown by the wind, whereas the rachis is persistent in Agrostis. Two features which distinguish Lachnagrostis from many, though not all, spp. of Agrostis are the well-developed callus hairs and the soft hairs on the lemma (though in a few spp. of Lachnagrostis the lemma is glabrous). Spp. of Lachnagrostis can be further distinguished from endemic and indigenous spp. of Agrostis by the well-developed palea and well-developed hairy rachilla.

The N.Z. spp. were revised by Edgar, E. N.Z. J. Bot. 33: 1-33 (1995), who briefly compared Lachnagrostis with Deyeuxia and Calamagrostis.