| # The grass genera of the world |

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

### Sohnsia Airy Shaw

Including Calamochloa Fourn.

Habit, vegetative morphology. Perennial; caespitose (forming tough clumps). Culms 30–100 cm high; herbaceous; unbranched above. Culm nodes hairy (or at least, hairy below the nodes). Leaves auriculate (from the sheath), or non-auriculate. Leaf blades linear (glaucous); narrow; flat, or rolled (becoming involute when dry); without abaxial multicellular glands; without cross venation; disarticulating from the sheaths (the lower sheaths persistent). Ligule a fringed membrane to a fringe of hairs (a ciliate rim).

Reproductive organization. Plants dioecious; without hermaphrodite florets (the stamens of pistillate plants seemingly sterile). The spikelets all alike in sexuality; female-only, or male-only. Plants outbreeding.

Inflorescence. Inflorescence of spicate main branches (the males and females similar); contracted. Primary inflorescence branches 6–12. Inflorescence with axes ending in spikelets (?). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. The racemes spikelet bearing to the base. Spikelet-bearing axes persistent. Spikelets pedicellate.

Female-sterile spikelets. The male spikelets 3–5 flowered, the rachilla not disarticulating; glumes equal, lemmas 3-awned; stamens 3, well developed, the pistil rudimentary. Rachilla of male spikelets prolonged beyond the uppermost male floret. The male spikelets with glumes; 3–5 floreted. The lemmas 3 awned. Male florets 3–4 (?); 3 staminate.

Female-fertile spikelets. Spikelets 10–12 mm long; abaxial; compressed laterally, or not noticeably compressed (?); disarticulating above the glumes; not disarticulating between the florets (the florets usually falling together); with conventional internode spacings (the rachilla joints short). Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus present. Callus short.

Glumes two; more or less equal (‘subequal’); shorter than the spikelets; shorter than the adjacent lemmas; dorsiventral to the rachis; hairless (scaberulous on the keel and towards the tip, otherwise glabrous); pointed; awnless; carinate; similar. Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1 (the third, terminal floret being incomplete); merely underdeveloped.

Female-fertile florets 2. Lemmas not becoming indurated; incised; 3 lobed, or 5 lobed (?); deeply cleft; awned. Awns 3; median and lateral; the median similar in form to the laterals; dorsal (from between two hyaline lobes); from near the top (from the back of the median lobe); non-geniculate; recurving; hairless (antrorsely scabrous); about as long as the body of the lemma; entered by one vein. The lateral awns shorter than the median to about equalling the median. Lemmas hairy (pilose marginally, and on each side of the median nerve above the base of the diverging median awn); 3 nerved, or 5 nerved (or more?). Palea present; relatively long (almost equalling the lemma); obscurely apically notched; awnless, without apical setae; 2-nerved; 2-keeled. Palea keels narrowly winged. Lodicules present; 2; free; fleshy (seemingly cuneate); glabrous. Stamens 3 (but apparently sterile). Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea. Pericarp fused.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals much narrower); of similar wall thickness costally and intercostally (of medium thickness). Mid-intercostal long-cells rectangular; having markedly sinuous walls (the sinuosity coarse, irregular). Microhairs present; elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhair basal cells 30 microns long. Microhair total length/width at septum 3.5. Microhair apical cell/total length ratio 0.3. Stomata common. Subsidiaries non-papillate; dome-shaped to triangular (often rather flat topped). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare; not paired. Intercostal silica bodies absent. Bulbous prickles with reduced points abundant over the veins. Costal short-cells conspicuously in long rows. Costal silica bodies present and well developed; present in alternate cell files of the costal zones; saddle shaped.

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4. The anatomical organization conventional. XyMS+. PCR sheath outlines even. PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially. PCR sheath extensions absent. PCR cell chloroplasts centripetal (very clearly so, even in the dried material seen). Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells (the broad columns of large cells, 2–3 cells wide, between all adjacent veins). Leaf blade with distinct, prominent adaxial ribs to ‘nodular’ in section; with the ribs more or less constant in size (large, broad, flat to broadly round topped, one over each bundle). Midrib not readily distinguishable; with one bundle only. Bulliforms not present in discrete, regular adaxial groups (in that they are not distinguishable from the colourless columns). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with every bundle); forming ‘figures’ (large I’s, which interrupt the PCR sheaths top and bottom). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

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

Distribution, phytogeography, ecology. Mexico.

Xerophytic; species of open habitats. Dry hillsides.

References, etc. Morphological/taxonomic: Sohns 1956. Leaf anatomical: studied by us.

Special comments. Fruit data wanting.

Illustrations. • Sohnsia filifolia, abaxial epidermis of leaf blade: this project. • Sohnsia filifolia, 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: 15th June 2025. delta-intkey.com’.

Contents