Diplacrum pygmaeum (R.Br.) Nees ex Boeckeler

Wilson, Karen L. & Barrett, Russell L., 2023, Revision of the tropical genus Diplacrum (Cyperaceae: Bisboeckelereae) in Australia, Australian Systematic Botany 36 (2), pp. 143-156 : 151-154

Diplacrum pygmaeum (R.Br.) Nees ex Boeckeler , Linnaea 38(4): 434 (1874)

Scleria pygmaea R.Br., Prodr. 240 (1810). Hypoporum pygmaeum (R.Br.) Nees , Linnaea 9: 303 (1834).

Type citation: ‘(T.) B. v.s.’ Type: Queensland: Endeavour River , July–Aug. 1770, J. Banks and D. Solander (lecto BM000900962; probable isolecto BM 000900963, BRI-AQ0341623, NSW 268828, P 00601916, P 00601917; fide K.L. Wilson in D.J. Mabberley and D.T. Moore, Regnum Veg. 160: 232 (2002)).

Sphaeropus pygmaeus Boeckeler , Flora 56: 89 (1873).

Type citation: ‘ Fr. Schulz pl. Austral. no. 260 – (Herb. Berolin.) … Nova Holland., Adelaide .’ Type: Northern Territory : Port Darwin, F. Schultz 260; holo B?, n.v.; iso MEL 2297608 .

Dwarf herbaceous annual, glabrous, 2–15 cm high, with reddish fibrous roots. Culms tufted, more or less erect or spreading. Leaves shorter than inflorescences; leaf blades flat, midrib prominent abaxially, glabrous, margins with minute antrorsely aculeate prickle hairs towards apex, 1.0– 2.5 mm wide at mid-length, with mid-nerve and 2 or more lateral nerves prominent on adaxial surface, mid-nerve prominent on abaxial surface; no ligule or expanded contraligule (the top of the leaf sheath opposite the junction with the blade truncate, not thickened); sheaths reddish at the base. Inflorescence much longer than the culms, with internodes 2–20 mm long, composed of 2–6 remote axillary clusters of spikelets; each cluster with 0–2 basal male spikelets and an upper female spikelet. Involucral bract at each node leaf-like, usually much longer than inflorescence. Male spikelets 1.0– 1.3 mm long, with 1 slender, more or less hyaline glume 1.0– 1.3 mm long, not indurated at maturity; stamen 1; anther ~ 0.2 mm long, with apical appendage <0.1 mm long. Female spikelets 2.0– 3.2 mm long, with 2 glumes encircling the ovary but not tightly clasping the nutlet nor falling with it; peduncle thickened at apex and cup-like at maturity; glumes with narrow hyaline margins, 2.2–3.0 mm long, including somewhat excurved awn 0.8–1.2 mm long, nearly as long as the body of the glume, 3-nerved (usually only mid-nerve prominent, narrow–elliptical with broad–acute apex, green turning straw-coloured with maturity, margins hyaline. Disc trigonous to circular, dark grey to blackish, with 6 off-white fine lines radiating from the centre, adhering to the nut. Style 3-fid. Nutlet globose, circular to subtrigonous in cross-section, glabrous, glossy, off-white maturing to dark purplish to blackish, slightly paler at apex, with 3 slightly paler longitudinal ribs and 3 paler swollen lobes at the base (adjacent to the disc) with a narrow yellowish-brown line between the lobes, 0.6–0.7 mm long, 0.5–0.6 mm in diameter, minutely colliculate or papillose, often more or less rugose when young ( Fig. 5 ).

Distribution and habitat

Widespread in tropical Australia, from the West Kimberley east to around Rockingham Bay in Queensland ( Fig. 1 d ). Grows in seasonally damp sands and loams, on the margins of swamps with a wide range of herbaceous species.

Conservation status

Widespread, including in national parks, so not considered at risk. We suggest a status of ‘Least Concern’ (International Union for Conservation of Nature 2019).

Notes

This species is similar in habit to D. blakei and D. latzii , differing most obviously in the more or less globose nutlet and the longer awn on the female glumes. D. caricinum also has a globose nutlet, but it differs from D. pygmaeum in the nutlet falling tightly clasped by the two glumes and in having a generally taller habit, with an elongated inflorescence.

Specimens examined

WESTERN AUSTRALIA: Mainland 8.3 km SE of Gertrude Cove on Kiska Island, N of Roe River mouth, West Kimberley , 23 Apr. 2008, M.D. Barrett and R.L. Barrett MDB 1988 ( PERTH 9339256 ) ; 18.3 km WNW of Munja Airstrip, Harding Range, West Kimberley , 22 Apr. 2008, M.D. Barrett and R.L. Barrett MDB1923 ( PERTH 9339132 ) ; ‘ Skull Creek’ camp and trap site, Doongan Station , 24 Apr. 2008, R.L. Barrett RLB4671 ( PERTH) ; beside King Edward River crossing on old Mitchell River Station Road, Doongan Station , North Kimberley , 28 Apr. 2007, R.L. Barrett RLB5823 ( PERTH) ; Youwanjela pavement 1, 26.7 km E of Kings Cascades; 12.4 km NNE of junction of Youwanjela Creek and Prince Regent River , Prince Regent Nature Reserve , 25 Jan 2007, R.L. Barrett and M.D. Barrett RLB7264 ( PERTH 8824258 ) ; DMR 008 site, 7 km SE of King Edward River on old Mitchell River Road, 30.7 km NW of Doongan Homestead, 18 May 2011, R.L. Barrett RLB7264 ( PERTH 9338012 ) ; 1.5 km W of Lennard River Gorge turn-off, Gibb River Road, 24 July 1974, G.W. Carr 4101 and A.C. Beauglehole 47879 (DNA NT50726, PERTH 1299034 ) . NORTHERN TERRITORY: Darwin and Gulf: Western Arnhem Land , ~ 94 km ESE of Jabiru, 20 Mar. 2000, I.D. Cowie 8680 (DNA D01411676 n.v., NSW 537187 ) ; ~ 10 km NE ‘ Mudginbarry’ [sic; Mudginberri] on Oenpelli road, 1 June 1974, S.W.L. Jacobs 1806 (CANB 257416, K, NSW 1119254, NT, P, READING); Mt Brockman Outlier , 15 km SE of Jabiru, 20 Apr. 1989, R.W. Johnson 4765 (BRI n.v., DNA n.v., NSW 470746 ) ; Lake Deane, 26 May 1973, P.K. Latz 3700B (NT 40591, p.p.); Cox River Station , 4 July 1977, P.K. Latz 7225 (DNA, NSW 2314168 ) ; Fish River block, 15 Apr. 2010, D.L. Lewis 1330 (DNA n.v., LD, NSW 928734 ) ; 4.2 km towards Ramingining from Central Arnhem Road , 22 July 1999, P.S. Short 4989 and R.K. Harwood (DNA, NSW 675668 ) ; South Bay, Bickerton Island, in the Gulf of Carpentaria , 19 June 1948, R.L. Specht 624 (CANB 29135, MEL 2204177, NSW 1119253, PERTH 2331985 ) ; track to Winmurra Billabong from Oenpelli Road, 6 May 1983, K.L. Wilson 5163 (DNA, H, K, NE, NSW 840767, P); Barramundie Gorge , 20 May 1987, K.L. Wilson 7305 ( NSW 206397 ) ; Graveside Creek , 24 May 1987, K.L. Wilson 7392a ( NSW 1119295 ) ; Red Lily Lagoon, Kapalga , 28 May 1987, K.L.Wilson 7457 ( NSW 196723 ) ; 19 km N of Arnhem Highway on track to Four Mile Hole , 30 May 1987, K.L. Wilson 7477 ( NSW 196743 ) . QUEENSLAND: Cook: near Cooktown , 17 May 1970, S.T. Blake 23354 (BRI, NSW 1119247 ) ; east bank of Little Laura River , S of Laura, 20 May 1975, N. Byrnes 3425 (BRI, NSW 225743 ) ; Codroy Creek 5.3 km N of Hann River on Laura to Musgrave road, 1 June 1989, J.R. Clarkson 8037 and V.J. Neldner (BRI-AQ591471 n.v., K n.v., NSW 2314174 ) ; 37 km SSE of Aurukun, ~ 12 km E of the Archer River , 28 May 1982, J.R. Clarkson 4387B (BRI-AQ0367052 n.v., K n.v., NSW 2314173 ) ; Browns Creek on Iron Range Road (174 km [~ 108 miles] N of Coen by road, 13 Sep. 1975, R.G. Coveny 7095b and P.D. Hind ( NSW 1119248 ) ; Bulleringa National Park, 80 km NW of Mount Surprise, Donkey Spring Creek , 23 Apr. 1998, P.I. Forster PIF22528 and R. Booth (BRI n.v., NSW 461971 ) ; ~ 5 km N of Ayton, Cooktown road, 22 May 1976, S.W.L. Jacobs 2734 and A.N. Rodd (BRI, NSW 1119252 ) ; W of Petford , 23 May 2009, B.S. Wannan 5660 and J. Beasley (BRI, NSW 823068 ) ; Dulhunty River crossing, 18 km SW of Heathlands base (by road), 6 Mar. 1992, K.L. Wilson 8253 and P. Sharpe (DNA, MBA, NSW 339173 ) . North Kennedy: Rockingham Bay , J. Dallachy s.n. (NSW 1119246 ex MEL) .

Figures

Fig. 5. Diplacrum pygmaeum. (a) Habitat. (b–e) Habit. (f) Thickened cup-like apex of peduncle (indicated by arrow). (g) Nutlets. Vouchers: (a–c) R.L. Barrett RLB5823 (PERTH); (d) S.W.L. Jacobs 1806 (NSW); (e, g) S.T. Blake 23354 (NSW); (f) P.S. Short and R.K. Harwood 4989 (NSW). Scale bars: 1 cm (d, e), 1 mm (f, g). Photos: R.L. Barrett.

Fig. 1. Distribution of Diplacrum species in Australia and Papua New Guinea based on data from the Australasian Virtual Herbarium (see https://avh.ala.org.au/, accessed June 2022). (a) D. caricinum. (b) D. blakei. (c) D. latzii. (d) D. pygmaeum.