Tuberous Bulrush

The earliest known collections of Bolboschoenus glaucus in North America, one a rice-field weed in Colusa County, California, and the other from Long Island, New York, are both dated 1923. The reports (as Scirpus tuberosus Desfontaines) from Quebec and Alabama are based on misidentifications.

Bolboschoenus glaucus was confused with B. maritimus worldwide until recently (J. Browning et al. 1995, 1997; S. G. Smith 1995). The name Scirpus tuberosus Desfontaines (= S. maritimus Linnaeus var. tuberosus (Desfontaines) Roemer & Schultes) was misapplied to B. glaucus by A. H. Beetle (1942) and T. Koyama (1962b). Putative B. glaucus × B. maritimus hybrids are locally common at Lake Lowell near Nampa, Canyon County, Idaho, and in California, where B. glaucus and putative hybrids are common weeds of rice fields and are cultivated with B. maritimus as food for waterfowl (J. Browning et al. 1995). Some specimens of B. maritimus from Long Island, New York, where B. glaucus has also been collected, suggest introgression from B. glaucus.

Oteng-Yeboah (Notes Roy. Bot Garden Edinburgh 33: 311-316, 1974) drew attention to the importance of the shape and anatomy of the fruit in infrageneric classifiaction of Bolboschoenus. His observations were extended to species represented in the area of the flora of southern Africa by Browning and Gordon-Gray (S. African J. Bot. 59: 311-318, 1993) and later to Pakistan (Browning, Gordon-Gray and Smith, l.c., 1995). In Flora Iranica B. maritimus (L.) Palla was considered to be present in Pakistan. Anatomical study of all fruiting specimens showed, however, the epicarp cells of nut to be isodiametric and not radially elongated as in NW European B. maritimus (Smith & Kukkonen, Taxon 48: 355-357, 1999). As the presence of B. maritimus in Pakistan could not be proven, it was consequently decided to assign all Pakistan material to B. glaucus. The identity of the plants, B. glaucus, used for plate 87 given by Hooper in Fl. Iraq 8: 377 (1985, as B. maritimus) is kindly confirmed by Dr. Jane Browning.

Culms to 150 cm × 1.5–3 mm. Leaves: sheaths reaching ± to middle of culm, fronts truncate to convex, membranous at mouth, veins diverging proximal to apex leaving acutely triangular veinless area; widest blade 2–6 mm wide. Inflorescences subumbellate, all or most spikelets solitary or in clusters of 2–7 on 3–11 rays, rays not exceeding 9 cm; involucral bracts that surpass inflorescence 1–3, widest bract 2–3 mm wide. Spikelets 3–30, ovoid to narrowly lanceoloid or cylindric, 10–40 × 3–5 mm; scales loosely imbricate, orange-brown to stramineous, 5–6 × 2.5 mm, membranous, transparent, apex 2-fid 0.5–1 mm deep, awns slender, 1–2 × 0.25 mm at base. Flowers: perianth bristles mostly tightly attached to shed achene, medium brown, much shorter than to equaling achene; anthers yellow, 3 mm; styles (2–)3-fid. Achenes pale brown to blackish brown, cuneate-obovate, clearly to obscurely trigonous or some thickly biconvex, angles rounded, 2.5–3.3 × 1.3–2.3 mm, apex rounded, beak minute, surface glossy, exocarp cells not evident at 20X, in cross section 1/3 of mesocarp thickness, cells isodiametric; achene specific gravity greater than water. 2n = 110 (Czech Republic).

Perennial, 20-30 cm. Rhizome creeping or with stolons ending with tubers, c. 7 mm diam. Stem 1-1.5 cm diam., sharply trigonous, even narrowly winged above, smooth or slightly scabrous, gryish green. Leaves as long as stem or longer; sheaths up to 10 cm, yellowish brown, soft, margin almost straight; blades to 25 cm long, 1-2.5 mm wide, flat, folded or recurved, keeled, grey green, smooth. Inflorescence up to 25 mm long, small multiple spike of 1-4 spikes; lateral spikes each with peduncles to 12 mm long; lowest bract longer than inflorescence. Spikes 6-12 x 4-6 mm, ovoid or globular, brown; tubular prophyll up to 5 mm, white, scarious; glumes 4-6 x 2-2.5 mm, cymbiform, more or less hairy, brown, sides nerveless, widely scarious, apex truncate, trifid, eroded, scarious, arista to 1,5 mm, straight to slightly recurved. Perianth bristles 4-6, c. half of the nut, persistent; stigmas 3. Nut 2.5-3 x 1.4-1.7 mm, obovoid, planoconvex, trigonous with rounded dorsal edge, brown to dark brown, apex conical, surface finely reticulate, glossy, epidermal cells small.

introduced; Calif., Idaho, N.Y., Oreg.; Eurasia; Africa.

Distribution: From Senegal and S. Africa to Pakistan; introduced to N. America.

Fl. Per.: (Febr.-) Sept.(-Oct.).

Fruiting summer.

Fresh to brackish shores and marshes, rice fields, waste places; 10–800m.

In "Scirpus-community" of shallow waters in brooks, rivers and lakes, also artificial depressions.

Scirpus glaucus Lamarck in J. Lamarck and J. Poiret, Tabl. Encycl. 1: 142. 1791

Scirpus glaucus Lam., Tabl. Encycl. 1: 142. 1791; Browning & al. in Brittonia 47: fig. 1, I-L. 1995.

maritimus: maritime, of the sea