| # The grass genera of the world |

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

### Willkommia Hackel

Named for H.M. Willkomm.

Including Willbleibia Herter

Habit, vegetative morphology. Annual, or perennial; stoloniferous, or caespitose. Culms 20–40 cm high; herbaceous; unbranched above. Culm nodes glabrous. Culm internodes hollow. Plants unarmed. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; 2–4 mm wide; flat; exhibiting multicellular glands abaxially. The abaxial leaf blade glands on the blade margins and intercostal. Leaf blades without cross venation; persistent. Ligule a fringe of hairs. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; exposed-cleistogamous, or chasmogamous (?).

Inflorescence. Inflorescence of spicate main branches; non-digitate (the spikes scattered along a central axis). Primary inflorescence branches 3–8. Rachides flattened and winged. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets secund (on one side of the rachis); biseriate; very shortly pedicellate.

Female-fertile spikelets. Spikelets about 4 mm long; adaxial; compressed dorsiventrally; disarticulating above the glumes; with a distinctly elongated rachilla internode between the glumes and with a distinctly elongated rachilla internode above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent. Callus pointed.

Glumes two; very unequal (G1 about two-thirds the length of G2); (the upper) long relative to the adjacent lemmas (slightly exceeding the spikelet); dorsiventral to the rachis; hairless (glabrous to scabrid); pointed (somewhat, in G2), or not pointed (blunt to slightly notched, G1); awnless; non-carinate (rounded); similar (thin, the G1 flimsier). Lower glume 0 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.

Female-fertile florets 1. Lemmas less firm than the glumes to similar in texture to the glumes; not becoming indurated; entire; pointed; awnless (but acuminate), or mucronate to awned. Awns when present, 1; apical; non-geniculate; hairless; much shorter than the body of the lemma; entered by one vein. Lemmas hairy; non-carinate (but the median nerve slightly prominent); without a germination flap; 3 nerved. Palea present; relatively long (glabrous or silky-hairy); entire to apically notched (minutely trilobed); awnless, without apical setae; not indurated (thinly membranous, flimsy); 2-nerved; 2-keeled. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers relatively long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit ellipsoid. Hilum short. Embryo large; with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae not over-arching the stomata (or scarcely so); consisting of one oblique swelling per cell, or consisting of one symmetrical projection per cell. Long-cells markedly different in shape costally and intercostally (costals much longer, much narrower). Intercostal zones exhibiting many atypical long-cells to without typical long-cells (the long-cells short to very short). Mid-intercostal long-cells rectangular; having markedly sinuous walls to having straight or only gently undulating walls. Microhairs present; more or less spherical; clearly two-celled; chloridoid-type (but the apical cell thin-walled). Microhair apical cell wall thinner than that of the basal cell and often collapsed. Microhairs 27–30 microns long. Microhair basal cells 15 microns long. Microhairs 17.4–19.5 microns wide at the septum. Microhair total length/width at septum 1.5–1.7. Microhair apical cells 9–12 microns long. Microhair apical cell/total length ratio 0.3–0.42. Stomata common; 18–21 microns long. Subsidiaries dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare. Intercostal silica bodies absent. Costal zones with short-cells. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; predominantly saddle shaped; not sharp-pointed.

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

C4; XyMS+. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. Leaf blade ‘nodular’ in section to adaxially flat (with slight abaxial ribs). Midrib conspicuous (via a larger bundle and sclerenchyma mass); with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (mostly), or associated with colourless mesophyll cells to form deeply-penetrating fans (few of these). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the large bundles); forming ‘figures’ (the large bundles). 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; Traginae. 2 species.

Distribution, phytogeography, ecology. 1 in southern U.S.A., 3 in southern Africa.

Xerophytic. Open habitats in savanna, usually halophytic.

References, etc. Leaf anatomical: studied by us - W. sarmentosa Hack.

Special comments. Fruit data wanting.

Illustrations. • Willkommia texana: Hitchcock and Chase (1950). • General aspect (W. sarmentosa): Gibbs Russell et al., 1990. • Willkommia sarmentosa, abaxial epidermis of leaf blade: this project. • Willkommia sarmentosa, abaxial epidermis of leaf blade detail: 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’.

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