| # The grass genera of the world |

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

### Desmostachya (Hook. f.) Stapf

From the Greek desmos (binding material) and stachys (a plant with a narrow inflorescence), perhaps alluding to sandbinding habit.

Including Stapfiola Kuntze

Habit, vegetative morphology. Perennial; rhizomatous and caespitose. Culms herbaceous. Culm nodes glabrous. Leaves non-auriculate. Leaf blades narrow; without abaxial multicellular glands; without cross venation; persistent. Ligule a fringed membrane to a fringe of hairs.

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

Inflorescence. Inflorescence of spicate main branches (narrow, dense, of many racemes, on an elongate axis); contracted; spicate. Inflorescence with axes ending in spikelets. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets secund; biseriate; sessile; densely imbricate.

Female-fertile spikelets. Spikelets 4–6 mm long; adaxial; compressed laterally; falling with the glumes; not disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus absent.

Glumes two; very unequal; shorter than the spikelets; shorter than the adjacent lemmas; free; dorsiventral to the rachis; pointed; awnless; carinate; similar (membranous, oval). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. Spikelets without proximal incomplete florets.

Female-fertile florets 6–16. Lemmas deltoid; decidedly firmer than the glumes (papery to leathery); not becoming indurated; entire; pointed; awnless; hairless; glabrous; carinate; 3 nerved. Palea present; relatively long; apically notched; 2-nerved. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; ellipsoid; compressed dorsiventrally, or not noticeably compressed. Hilum short. Pericarp fused. Embryo large; not waisted.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals much longer); of similar wall thickness costally and intercostally (fairly thick walled). Intercostal zones with typical long-cells (but the interstomatals very regularly cross shaped). Mid-intercostal long-cells rectangular; having markedly sinuous walls (pitted). Microhairs present; elongated; clearly two-celled; panicoid-type to chloridoid-type (basal cells fairly long, apical cells rather thin walled, variable, ranging from unexceptional chloridoid type to broad panicoid type - cf. Eragrostis?). Microhair apical cell wall thinner than that of the basal cell but not tending to collapse. Microhairs (27–)30–33(–42) microns long. Microhair basal cells 24 microns long. Microhairs 9–12 microns wide at the septum. Microhair total length/width at septum 2.5–3. Microhair apical cells 9–16 microns long. Microhair apical cell/total length ratio 0.35–0.4. Stomata common; 15–18 microns long. Subsidiaries triangular. Intercostal short-cells common; in cork/silica-cell pairs and not paired (i.e. in ones and twos); silicified. Intercostal silica bodies imperfectly developed; slightly saddle shaped, or tall-and-narrow, or crescentic. Costal short-cells conspicuously in long rows. Costal silica bodies 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; XyMS+. PCR sheath outlines even (despite conspicuous adaxial extension cells). PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially and interrupted laterally. PCR sheath extensions present. Maximum number of extension cells not conventionally determinable, the PCR sheaths being interrupted by large colourless cells and sclerenchyma. PCR cell chloroplasts centrifugal/peripheral (seemingly, in bipinnata). Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (these incorporated in the traversing colourless girders). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); forming ‘figures’ (all bundles with I’s). Sclerenchyma not all bundle-associated. The ‘extra’ sclerenchyma in abaxial groups and in adaxial groups (comprising small groups at the bases of the colourless columns, and a more or less continuous adaxial layer). The lamina margins with fibres.

Cytology. Chromosome base number, x = 10. 2n = 20.

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

Distribution, phytogeography, ecology. Northeast tropical Africa to India.

Species of open habitats. Arid regions.

Economic aspects. Significant weed species: D. bipinnata.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia striiformis and ‘Uromyces’ eragrostidis.

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

Illustrations. • Desmostachya bipinnata: Bor, Fl. of Iraq (1968). • Desmostachya bipinnata,abaxial epidermis of leaf blade: this project. • Desmostachya bipinnata, leaf blade TS: 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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