Flora of New Zealand Series

; Holotype: CHR 313063! A. P. Druce near Lake Tennyson, North Canterbury, tarn margin, 3700 ft, Jan 1976.

Reddish green tufts 18-30 cm, with erect culms topped by dense cylindric panicles and much exceeding the leaves at maturity; branching extravaginal. Leaf-sheath chartaceous, glabrous, light green to light reddish brown, ribs more prominent above. Ligule 2-3 mm, erose, often tapered centrally to a fine tip, abaxially glabrous. Leaf-blade 2-9 cm × 1.5-2 mm, folded, abaxially smooth, adaxially slightly ribbed, sparsely scabrid on ribs; margins finely scabrid, tip hooded. Culm 10-24 cm, erect or geniculate at base, nodes hidden by leaf-sheaths, internodes glabrous. Panicle 1.5-4.5 cm × 5-8 mm, cylindric, dense; rachis smooth, branches and pedicels rather sparsely finely scabrid. Spikelets 5-7 mm, purplish green. Glumes subequal, 1-nerved, submembranous, elliptic-lanceolate, acute, smooth, keel finely scabrid on upper ⅔. Lemma 4-5 mm, ⅔-⅘ length of glumes, subcoriaceous, smooth below, finely papillose to prickle-toothed above, ± elliptic, apex shortly bifid; awn 3.5-4.5 mm, from upper ¼ of lemma, twisted about twice at base, ± recurved above. Palea c. ⅔ length of lemma, hyaline, keels thickened, faintly prickle-toothed above. Callus hairs 0.3-1 mm. Rachilla prolongation 0.5-1 mm, bearing minute hairs throughout except at glabrous tip. Lodicules 0.4-0.5 mm. Anthers 0.3-0.65 mm. Gynoecium: ovary 0.6 mm; stigma-styles 1.0-1.5 mm. Caryopsis c. 2 × 0.6 mm, with dehisced anthers entangled in stigmas. Cleistogamous.

S.: north-west Nelson at Lake Sylvester, and North Canterbury at Lake Tennyson. Lake margins on rocky ground or at tarn margins; 1120-1340 m.

Endemic.

In the dense cylindrical panicle D. lacustris resembles D. quadriseta and D. avenoides; in D. lacustris all specimens seen were cleistogamous, but D. quadriseta and D. avenoides may be chasmogamous or cleistogamous. The awn in D. lacustris arises much higher on the lemma than in the other two species; the rachilla is longer than that of D. quadriseta, and lacks the strong hair tuft of D. avenoides.