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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Scleropogon Phil.

From the Greek skleros (hard) and pogon (beard), alluding to hard awns.

Including Lesourdia Fourn.

Habit, vegetative morphology. Perennial; stoloniferous, or stoloniferous and caespitose. Culms 10–20 cm high; herbaceous. Leaves mostly basal; non-auriculate. Leaf blades linear; narrow; 1.5–2 mm wide; flat to folded (folded and arcuate above); without cross venation. Ligule a fringe of hairs (very short).

Reproductive organization. Plants monoecious with all the fertile spikelets unisexual, or dioecious; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant (monoecious, the male and female spikelets mixed or in separate panicles), or all alike in sexuality (dioecious); female-only, or male-only, or female-only and male-only. The male and female-fertile spikelets in different inflorescences, or mixed in the inflorescence. Plants outbreeding (at least when dioecious).

Inflorescence. Inflorescence few spikeleted; a single raceme (spike-like, with few spikelets), or paniculate (contracted, with few spikelets); contracted; spatheate (the glumes of female spikelets subtended by glume-like bracts); not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; shortly pedicellate, or subsessile; imbricate.

Female-sterile spikelets. Male spikelets with equal, lanceolate glumes separated by a short internode; 6–15 flowered; lemmas attenuate into short awns; 2 fleshy lodicules. Rachilla of male spikelets prolonged beyond the uppermost male floret. The male spikelets with glumes; 6–15 floreted. The lemmas shortly awned. Male florets 5–14 (?).

Female-fertile spikelets. Spikelets 25–30 mm long; compressed laterally to not noticeably compressed (narrowly cylindrical); disarticulating above the glumes; not disarticulating between the florets (the florets falling together as a cylindric, many-awned unit). Rachilla prolonged beyond the uppermost female-fertile floret. Hairy callus present (sharp-bearded, at the base of the lowermost floret and of the unit as shed).

Glumes two; very unequal; shorter than the spikelets; long relative to the adjacent lemmas (?); hairless; pointed; awnless; similar (hyaline, lanceolate-acuminate). Lower glume 1 nerved, or 3 nerved. Upper glume 3 nerved. Spikelets with incomplete florets (basal florets male, those above female or rarely hermaphrodite). The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1–2; paleate. Palea of the proximal incomplete florets fully developed. The proximal incomplete florets male. The proximal lemmas shortly awned; 3 nerved; exceeded by the female-fertile lemmas.

Female-fertile florets 1–3. Lemmas narrow; decidedly firmer than the glumes (cartilaginous); not becoming indurated; incised; 3 lobed, or 4 lobed (with a shallow median sinus, and a somewhat deeper cleft on either side); not deeply cleft; awned. Awns 3 (70–140 mm long extensions from the nerves, arising between small lobes); median and lateral; the median similar in form to the laterals; non-geniculate; hairless (scabrous); much longer than the body of the lemma. The lateral awns long. Lemmas hairless; non-carinate (rounded on the back); 3 nerved. Palea present (narrow, hairy at the base); tightly clasped by the lemma; entire (obtuse); awned (with 2 short awns); 2-nerved (the nerves near the margins); 2-keeled. Lodicules absent. Stamens 0. Ovary apically glabrous (?). Stigmas 2.

Fruit, embryo and seedling. Disseminule consisting of the abscised spikelet. Fruit medium sized (about 4.8 mm long); linear; not noticeably compressed. Hilum short. Pericarp fused. Embryo large; with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal (on the long-cells and interstomatals). Intercostal papillae over-arching the stomata (both at the ends and laterally); mostly consisting of one oblique swelling per cell. Long-cells markedly different in shape costally and intercostally (the costals narrower and more regularly rectangular); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; chloridoid-type (the basal cells relatively long); 57–60–66 microns long; 15–18–19.5 microns wide at the septum. Microhair total length/width at septum 2.9–4.4. Microhair apical cells 18–21 microns long. Microhair apical cell/total length ratio 0.3–0.35. Stomata common; 21–24–27 microns long. Subsidiaries high dome-shaped (mostly), or triangular. Guard-cells overlapped by the interstomatals (very slightly), or overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs and not paired (mostly paired, but often superposed and sometimes appearing solitary); silicified. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped, butterfly shaped, and dumb-bell shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS+. PCR sheath outlines even. PCR sheath extensions absent. Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section to adaxially flat (with slight, rounded abaxial ribs). Midrib conspicuous (via its prominent, rounded abaxial keel); with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); forming ‘figures’ (all the bundles with ‘anchors’). Sclerenchyma all associated with vascular bundles (apart from small marginal fibre groups).

Cytology. Chromosome base number, x = 10. 2n = 28 and 40.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Scleropogoninae. 1 species (S. brevifolius).

Distribution, phytogeography, ecology. Southwest U.S.A. and northern Mexico, Chile and Argentina.

Xerophytic; species of open habitats. Dry grassy plains.

Economic aspects. Important native pasture species: S. brevifolius.

Rusts and smuts. Rusts — Puccinia.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us.

Illustrations. • S. brevifolius: Nicora & Rúgolo de Agrasar (1987). • S. brevifolius, abaxial epidermis of leaf blade: this project. • S. brevifolius, TS leaf blade: this project

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 11th December 2017.’.