14. Bromus willdenowii Kunth (rescue grass)

Pl. 137 c, d; Map 569

Plants annual (in Missouri), forming tufts. Flowering stems 30–100 cm long, erect or ascending, mostly glabrous. Leaves 6–10 per stem. Leaf sheaths mostly loosely overlapping, hairy, the tip strongly concave (V‑shaped), without auricles. Leaf blades 3–20 cm long, 3–12 mm wide, usually hairy, dull on the undersurface. Inflorescences open panicles with numerous spikelets, the branches mostly ascending at maturity, the stalks of the spikelets longer than or shorter than the spikelets. Spikelets 18–32 mm long, strongly compressed laterally at maturity, with 4–12 florets. Lower glume 7–12 mm long, lanceolate, 5‑ or 7‑nerved, strongly keeled on the back, glabrous but roughened along the nerves. Upper glume 9–13 mm long, lanceolate, 7‑ or 9(11)‑nerved, strongly keeled on the back, the margins not inrolled at maturity, glabrous but roughened along the nerves. Lemmas 11–20 mm long, elliptic, strongly keeled on the back, 11–15‑nerved, glabrous but roughened along the nerves, the apical teeth 0.1–0.3 mm long, awnless or the awn 0.5–3.0 mm long, straight. Paleas shorter than the lemmas. Anthers 1–4 mm long. Fruits 7–8 mm long, circular in cross‑section to somewhat flattened or slightly V‑shaped, the longitudinal groove narrow and shallow. 2n=28, 42, 56. April–July.

Introduced, uncommon and widely scattered in Missouri (native of South America, widely introduced farther north). Railroads and open, disturbed areas.

The proper scientific name for rescue grass remains controversial. Originally, the name B. catharticus Vahl was assigned to these plants, but they have been called B. unioloides Kunth and B. willdenowii by various authors. Raven (1960) summarized earlier studies of artificially produced hybrids in the complex and studied type specimens of the last two names. He concluded that the complex consisted of two species native to South America, both of which have been introduced into the United States, but that the common rescue grass corresponded to the name B. willdenowii. He applied the name B. unioloides to the other taxon. Pinto‑Escobar (1976) restudied type specimens in the complex and concluded that the name B. catharticus was the oldest name for the taxon that Raven (1960) referred to as B. unioloides. Concurrently, several authors (including Pinto‑Escobar, 1981) studying native populations in South America were unable to differentiate two species, based on differences noted by Raven for the type specimens. Thus, the unresolved taxonomic problem, which requires further study, is whether the complex contains one or two species. The present treatment tentatively follows Raven’s (1960) assessment of two species; those who prefer to accept only a single taxon should use the name B. catharticus.

This early flowering species is cultivated as a winter and spring pasture grass in parts of the southern United States.