Grass Genera of the World

L. Watson and M. J. Dallwitz


Commelinidium Stapf

Sometimes referred to Acroceras

Habit, vegetative morphology. Commelinaceous perennial; rhizomatous to stoloniferous, or decumbent. Culms 10–90 cm high; herbaceous. Culm nodes glabrous. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Leaf blades ovate; broad; 15–40 mm wide; cordate, or not cordate, not sagittate; pseudopetiolate, or not pseudopetiolate; cross veined; disarticulating from the sheaths; a fringed membrane; short.

Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence of spicate main branches (spiciform racemes), or paniculate; open; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary, or paired; somewhat secund; pedicellate.

Female-fertile spikelets. Spikelets 4–6 mm long; abaxial; compressed dorsiventrally; falling with the glumes; with a distinctly elongated rachilla internode between the glumes. Rachilla prolonged beyond the uppermost female-fertile floret (as a minute vestige), or terminated by a female-fertile floret; the rachilla extension when present, naked. Hairy callus absent.

Glumes two (separated by a marked internode); very unequal; (the longer) long relative to the adjacent lemmas; free; dorsiventral to the rachis; hairless; pointed (with a small apical callosity); awnless; carinate; similar (membranous-herbaceous). Lower glume 3–5 nerved. Upper glume 5 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets reduced. The proximal incomplete florets sterile. The proximal lemmas similar to the glumes; awnless; 5 nerved; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas; not becoming indurated.

Female-fertile florets 1. Lemmas decidedly firmer than the glumes (leathery); smooth; not becoming indurated; entire; crested at the tip (cf. Acroceras, Cyrtococcum); awnless (but apiculate); hairless (shining); non-carinate; having the margins inrolled against the palea; with a clear germination flap; 7–9 nerved. Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved; keel-less. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary glabrous. Styles free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit small. Hilum short.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Intercostal zones exhibiting many atypical long-cells. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (60–)63–78(–79.5) microns long; 6.3–9 microns wide at the septum. Microhair total length/width at septum 7–12.4. Microhair apical cells 27–36 microns long. Microhair apical cell/total length ratio 0.42–0.46. Stomata common; 27–33 microns long. Subsidiaries high dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous; with one bundle only. Bulliforms not present in discrete, regular adaxial groups (constituting most of adaxial epidermis). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Special diagnostic feature. Plants not as in Dichanthelium (q.v.).

Cytology. 2n = 36.

Taxonomy. Panicoideae; Panicodae; Paniceae.

Distribution, ecology, phytogeography. 3 species; West tropical Africa. Shade species.

Paleotropical. African. Sudano-Angolan and West African Rainforest. Sahelo-Sudanian, Somalo-Ethiopian, and South Tropical African.

References, etc. Leaf anatomical: this project.

Illustrations. • Fruiting floret. Commelinidium gabunense. Thickened/inrolled lemma margins. • Germination flap. Commelinidium gabunense.


Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).

Index