VicFlora: Rytidosperma robertsoniae

Tufted perennial. Culms (9–)18–32(–44) cm high. Leaves with sparse to moderately dense hairs, occasionally glabrous, blade flat to inrolled, to 20 cm long and mostly 0.5–1.2 mm wide wide. Panicle ovate, oblong or broad-lanceolate, not or shortly exserted from sheath at seed maturity, mostly 3–8 cm long. Spikelets (5–)6–8(–9)-flowered; glumes subequal, acute, (14–)16–21(–25.5) mm long, pale amber near the midnerve and often with a slightly purple band near the hyaline margins; lemma narrow, (2.5–)3–4.5(–5) mm long, with 2 rows of hairs, the lower 1–1.5 mm above the callus hair-tuft; hair-tufts of the lower row next to the central rib absent, the callus hairs very short, often not reaching the junction of the lemma and callus, and never reaching the base of the lower row of hair-tufts on the lemma backs; lateral lobes erect, c. (7–)9–13(–14.5) mm long, acuminate, the flat part typically rather broad and abruptly tapering to the setae which are generally longer than the flat part; hyaline lobe margins (0.2–)0.4–0.6(–0.75) mm wide, broader than the opaque parts; central awn exceeding lateral lobes by (4.8–)6–9(–14) mm; palea narrow-lanceolate or narrow-elliptic, hyaline and deeply notched at apex, distinctly narrowed above the caryopsis into a long hyaline tip (25–)30–50(–60)% of the length, exceeding the sinus by (0.75–)1.5–2.4(–2.9) mm. Flowers mainly Sep.–Dec.

LoM, MuM. Also WA, SA, NSW. Confined to semi-arid areas. In Victoria, known from a few collections from the north-west part of the State (e.g. Neds Corner Station, Mildura, and Wyperfeld National Park).

Rytidosperma robertsoniae is a segregate of R. caespitosum. R. robertsoniae differs from R. caespitosum in the callus hairs being very short, often not reaching the junction of the lemma and callus and rarely reaching the base of the lower row of hair-tufts on the lemma-backs, whereas in R. caespitosum at least some of the callus hairs are long enough to overlap the lower row of hair-tufts on the lemma-back. The tip of the palea is also more deeply cleft than those of forms of R. caespitosum, (3–)4–7(–8)% of the palea. The hyaline margins of the lemma lobes are very broad in R. robertsoniae, whereas R. caespitosum has lobe margins that are usually about equal to or narrower than the width of the opaque part of the lobe. Additionally, R. robertsoniae has a chromosome number of 2n=24, while R. caespitosum generally has 2n=48, with occasional 2n=72 (Abele 1959).