Flora of New Zealand Series

prairie grass

Coarse green to yellowish green perennial tufts, 30-120 cm, with heavy panicles. Leaf-sheath keeled above, lower sheaths with fine, silky hairs, the hairs more scattered in upper sheaths. Ligule 3-5 mm, ± tapered, denticulate. Leaf-blade 15-40 cm × 8-15 mm, abaxially smooth, or minutely scabrid on ribs, adaxially with scattered fine hairs; margins finely scabrid, tip acute to acuminate. Culm stout, ascending to erect, internodes glabrous. Panicle 15-35 cm, erect or nodding above, pyramidal with scabrid branches in threes or pairs from the distant nodes; lower branches ascending, horizontal or sometimes drooping, upper branches ascending to erect. Spikelets 2.5-4 cm, 5-9-flowered, elliptic-oblong to ± cuneate, light green, sometimes purple-suffused. Glumes ± unequal, subacute to acute, keel minutely scabrid; lower 10-14 mm, 5-7-nerved, upper c. 15 mm, 9-nerved. Lemma 17-23 mm, 9-13-nerved, keeled, nerves scabrid, internerves smooth to slightly scabrid; awn 0.5-4-(5) mm. Palea c. ⅔ length of lemma or shorter. Callus with minute hairs. Rachilla scabrid or sparsely minutely pubescent. Anthers 0.5-1 mm in cleistogamous flowers, c. 4.5 mm in chasmogamous flowers. Caryopsis 7.1-7.2 × 1.5-2.2 mm. Fig. 12.

N.; S.: throughout; St.; K., Three Kings Is, Ch. Roadsides and waste ground.

Naturalised from South America.

REPRODUCTIVE BIOLOGY

Flowers of Bromus may be chasmogamous or facultatively cleistogamous and both types may occur on the same plant; stamens and lodicules are shorter in cleistogamous flowers. Chasmogamous flowers are produced in spring in favourable conditions with ample soil moisture whereas cleistogamous flowers are induced by longer day-length and adverse conditions [Harlan, J. R. Amer. J. Bot. 32: 66-72 (1945); Langer, R. H. M. and Wilson, P. New Phytol. 64: 80-85 (1965)]. Some species are wholly chasmogamous or cleistogamous; McKone, M. J. Amer. J. Bot. 72: 1334-1338 (1985) found that Bromus inermis was self-sterile and chasmogamous and that B. tectorum, known to be highly self-fertile, produced mostly cleistogamous flowers.

Forde, M. B. and Edgar, E. (1995 op. cit.) supported Raven, P. H. Brittonia 12: 219-221 (1960) in treating prairie grass as Bromus willdenowii Kunth. They recognised a slender Andean segregate as a distinct species, B. catharticus Vahl; Raven also accorded this brome specific rank but referred it to B. unioloides Kunth. Other agrostologists favour a single taxon, B. catharticus Vahl : e.g., Matthei, O. Gayana Bot. 43: 47-110 (1986); Veldkamp, J. F., Eriks, M. and Smit, S. S. Blumea 35: 483-497 (1991); and Petersen, P. M. and Planchuelo, A. M. Novon 8: 53-60 (1998).

Fig. 12 Bromus willdenowii S, spikelet, × 3.2; G 1, G 2, glumes, × 4; L, lemma dorsal view and flattened, × 4; P, palea dorsal view, × 4; Lo, lodicules, × 20; O, ovary, hairy appendage and stigmas, frontal and dorsal views, × 20; St, stamens, × 20. © All rights reserved. [Image: 4X7F]