| # The grass genera of the world |

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

### Hesperostipa (Elias) Barkworth

From the Greek esperis (western) and Stipa (q.v.).

~ Stipa

Including Sparteum P. Beauv.

Habit, vegetative morphology. Perennial; densely caespitose. Culms 30–100 cm high; herbaceous; branched above, or unbranched above (?). Culm nodes hairy, or glabrous (?). Culm internodes solid, or hollow (?). Young shoots intravaginal. Leaves mostly basal, or not basally aggregated (?); auriculate, or non-auriculate (?). Leaf blades linear; narrow; 1–5 mm wide; setaceous, or not setaceous; flat, or folded, or rolled (involute or convolute); not pseudopetiolate; without cross venation; persistent; rolled in bud, or once-folded in bud. Ligule an unfringed membrane, or a fringed membrane (?). Contra-ligule present, or absent (?).

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; inbreeding; exposed-cleistogamous, or chasmogamous, or exposed-cleistogamous and chasmogamous; with hidden cleistogenes, or without hidden cleistogenes (?). The hidden cleistogenes (if present) in the leaf sheaths (?).

Inflorescence. Inflorescence few spikeleted to many spikeleted (?); paniculate; not deciduous; open, or contracted (usually); with capillary branchlets, or without capillary branchlets (?); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 15.2–50 mm long (always more than 15 mm); not noticeably compressed (?); disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. The callus hairs white, or brown. Callus long (2.5–7 mm long); sharp pointed.

Glumes two; very unequal to more or less equal; about equalling the spikelets to exceeding the spikelets (?); nearly always long relative to the adjacent lemmas (?); pointed (lanceolate, long-acuminate); awned, or awnless (?); similar (lanceolate). Lower glume 1–4 nerved (? - ‘evident’). Upper glume 3–6 nerved (?). Spikelets with female-fertile florets only; without proximal incomplete florets.

Female-fertile florets 1. Lemmas narrowly cylindrical; not convolute (the margins tightly involute, not overlapping); not saccate; with an apical ‘crown’; decidedly firmer than the glumes; smooth (lacking abaxial-epidermal silica bodies); becoming indurated (horny); white in fruit to yellow in fruit (or cream); entire (the upper portion fused, without lobes); awned. Awns 1; median; apical; geniculate (bigeniculate); hairless, or hairy (but not long-plumose); much longer than the body of the lemma (50–200 mm long); entered by several veins (?); persistent. Lemmas sparsely hairy; non-carinate (terete); having the margins inrolled against the palea (the median zone of the palea exposed); without a germination flap; 3–7 nerved (?). Palea present; relatively long (subequal to the lemma); tightly clasped by the lemma; prow-tipped; awnless, without apical setae; thinner than the lemma, or textured like the lemma (?); indurated (more or less, at least the exposed part); 2-nerved (the veins extending to the apex); keel-less. Palea back glabrous (often), or scabrous, or hairy (?). Lodicules present; 3 (???); free; membranous (? stipoid); glabrous; not toothed. Stamens 3 (often short). Anthers 1.2–9 mm long (?); not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small, or medium sized, or large (?); fusiform; compressed laterally, or not noticeably compressed (?). Hilum long-linear. Embryo small; not waisted. Endosperm hard; without lipid; containing only simple starch grains, or containing compound starch grains (?). Embryo with an epiblast (the epiblast long and apically notched); without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.

Seedling with a short mesocotyl, or with a long mesocotyl (?). First seedling leaf with a well-developed lamina. The lamina narrow; erect; 3–5 veined (?).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally to markedly different in shape costally and intercostally (the costals narrower); of similar wall thickness costally and intercostally (fairly thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls (conspicuously pitted). Microhairs absent. Stomata common. Subsidiaries non-papillate; broadly parallel-sided to dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs and not paired (many solitary); silicified. Intercostal silica bodies imperfectly developed to present and perfectly developed; irregularly rounded to crescentic. Exhibiting numerous small prickles costally and intercostally. Costal short-cells predominantly paired. Costal silica bodies present and well developed to poorly developed; present throughout the costal zones; irregularly, imperfectly rounded, tall-and-narrow, and crescentic.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with radiate chlorenchyma to with non-radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs; with the ribs very irregular in sizes (alternately large and small). Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (these small, in the bases of the furrows); in simple fans. All the vascular bundles accompanied by sclerenchyma (except ajoining the blade margins). Combined sclerenchyma girders present; forming ‘figures’ (the large bundles with I’s, most of the small ones with ‘anchors’, I’s or T’s). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Cytology. Nucleoli disappearing before metaphase (?).

Classification. Watson & Dallwitz (1994): Stipoideae; Stipeae. Soreng et al. (2015): Pooideae; Stipeae. 5 species.

Distribution, phytogeography, ecology. North America.

Commonly adventive (?). Mesophytic to xerophytic; species of open habitats. Seasonally dry grasslands.

Economic aspects. Significant weed species: the pointed calluses of S. comata and S. spartea sometimes injure livestock.

Rusts and smuts. Rusts — Puccinia. Smuts from Tilletiaceae and from Ustilaginaceae (?).

References, etc. Morphological/taxonomic: Barkworth and Everett 1987; Barkworth 1993. Leaf anatomical: studied by us - H. comata only.

Special comments. This is an inadequate description of a Stipa segregate, consisting of S. comata, S. curtiseta, S. neomexicana and S. spartea. See further comment under Stipa sensu lato. Fruit data wanting.

Illustrations. • Hesperostipa spartea (as Stipa): Hitchcock and Chase (1950). • Hesperostipa spartea, awn TS: this project. Stipa (Hesperostipa) spartea. Awn with three vascular bundles.

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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