Bromus interruptus

Description

Bromus interruptus is an annual or biennial herb. Its slender to somewhat stout culms measure 20 to 100 cm and occur as either loosely tufted or solitary. They are erect, very lightly pubescent, unbranched and contain 2 to 4 nodes. The green leaves measure 6 to 20 cm long by 2 to 6 mm wide and are long-linear in shape with a pointed apex. They are covered in a soft pubescence. The leaf sheaths are tubular with the lower portion having a soft pubescence replaced by shorter hairs in the upper portion. The ligules measure 1 to 2 mm and are membranous and toothed. The inflorescence is a dense, oblong panicle that measures 2 to 9 cm in length and up to 20 mm thick. It is erect, greyish green in colour and, as the name suggests, usually interrupted, sometimes even reduced to a single spikelet. Its branches measure up to 15 mm in length. The sessile (i.e. without a stalk) or nearly sessile spikelets occur in dense clusters with each measuring 10 to 15 mm long by 5 to 8 mm broad. They are covered in soft pubescence and are plump with a broadly ovate (i.e. egg-shaped) to broadly oblong shape. Each contains 5 to 11 flowers and they slowly break up beneath each lemma once mature.The glumes, or sterile husks at the base of each spikelet, are unequal in morphology and persist after maturity. Both the upper and lower glumes may have apices ranging from blunt to abruptly pointed. The lower glume is 5 to 7 mm long with 3 to 7 veins and an oblong to elliptical outline. The upper one is slightly larger, measuring 6 to 9 mm long with 5 to 9 veins and an ovate to broadly elliptical shape. The lemmas, the outer of the two husks enclosing a flower, measure 7.5 to 9 mm long by 5 to 5.5 mm wide and have an obovate to obovate-elliptic outline. They have 7 to 9 prominent veins, 2 very small teeth, and membranous margins that are more flexible than the otherwise firm centre. Each lemma has a fine, rough awn that measures 4 to 8 mm and may be either be straight or bending. The paleas, the upper of the two husks that enclose a flower, are narrowly elliptical in outline and are shorter than the lemmas. They are bifid (i.e. split in two) to the base with the split keel being somewhat pubescent. The bifid paleas distinguish the interrupted brome from all other species in the genus.Each spikelet contains 5 to 8 flowers. The anthers are 1 to 1.5 mm long. The caryopsis is tightly enclosed and is narrowly ellipsoid in outline. The chromosome number is 2n = 28.