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The grass genera of the world

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

Bouteloua Lag.

Named for the brothers Claudio and Esteban Boutelou.

Including Actinochloa Roem. & Schult., Antichloa Steud., Aristidium (Endl.) Lindley, Atheropogon Willd., Chondrosum Desv., Erucaria Cerv., Eutriana Trin., Heterosteca Desv., Nestlera Steud., Pleiodon Reichenb., Polyodon Kunth, Triaena Kunth, Triplathera (Endl.) Lindley

Excluding Buchloë, Buchlomimus, Cathestecum, Cyclostachya, Griffithsochloa, Opizia, Pentarrhaphis, Pringleochloa, Soderstromia

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms (10–)15–80 cm high; herbaceous; branched above, or unbranched above. Culm internodes solid, or hollow. Leaves mostly basal, or not basally aggregated; non-auriculate. Leaf blades narrow; flat, or folded, or rolled; exhibiting multicellular glands abaxially. The abaxial leaf blade glands intercostal. Leaf blades without cross venation. Ligule a fringe of hairs.

Reproductive organization. Plants nearly always bisexual, all with bisexual spikelets, or dioecious (occasionally gynodioecious - B. chondrosoides); with hermaphrodite florets, or without hermaphrodite florets. The spikelets all alike in sexuality (usually), or of sexually distinct forms on the same plant; hermaphrodite, or female-only, or hermaphrodite and female-only. Plants outbreeding and inbreeding; exposed-cleistogamous, or chasmogamous. Apomictic, or reproducing sexually.

Inflorescence. Inflorescence of spicate main branches (the spikelets few to many), or a false spike, with spikelets on contracted axes (mainly in Section Atheropogon). Primary inflorescence branches borne biseriately on one side of the main axis. Inflorescence axes not ending in spikelets (the rachis of the ‘spike’ or cluster usually ending in a naked, straight or forked tip). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes disarticulating (in Section Atheropogon), or persistent (Section Chondrosum); when falling, falling entire. Spikelets (when on much reduced ‘branches’) subtended by solitary ‘bristles’; solitary; secund (on one side of rachis); biseriate.

Female-fertile spikelets. Spikelets compressed laterally; disarticulating above the glumes, or falling with the glumes (i.e., when the spikes shed). Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets.

Glumes two; very unequal (G1 shorter and narrower); (the longer) shorter than the adjacent lemmas, or long relative to the adjacent lemmas; hairy, or hairless; pointed (acuminate or awn-tipped); awned (shortly so), or awnless. Lower glume 1 nerved. Upper glume 1 nerved. Spikelets usually with incomplete florets. The incomplete florets when present, which is usual, distal to the female-fertile florets. The distal incomplete florets clearly specialised and modified in form (the rudiment(s) usually 3-awned, with the awns longer than those of the L1). Spikelets without proximal incomplete florets.

Female-fertile florets 1. Lemmas with nerves extending into short mucros or awns, with lobes or teeth between; not becoming indurated (membranous); incised; 1 lobed, or 2 lobed, or 3 lobed; not deeply cleft; awnless, or mucronate, or awned. Awns when present, 1 (sometimes with lateral mucros), or 3; median, or median and lateral; the median similar in form to the laterals (when laterals present); non-geniculate. The lateral awns when present, shorter than the median, or about equalling the median, or exceeding the median. Lemmas without a germination flap; 3 nerved. Palea present; awnless, without apical setae, or with apical setae, or awned (via excurrent nerves); 2-nerved. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers 0.4–4 mm long. Ovary apically glabrous. Stigmas 2.

Fruit, embryo and seedling. Fruit ellipsoid. Hilum short. Pericarp fused. Embryo large. Endosperm hard; without lipid. Embryo 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 absent. Long-cells differing markedly in wall thickness costally and intercostally (costals thicker walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical to elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs without ‘partitioning membranes’ (in B. curtipendula); 15.6–29 microns long. Microhair basal cells 12–18 microns long. Microhairs 7.5–10.5 microns wide at the septum. Microhair total length/width at septum 1.9–2.8. Microhair apical cells 7.5–12 microns long. Microhair apical cell/total length ratio 0.33–0.48. Stomata common; 21–24 microns long. Subsidiaries dome-shaped, or triangular. Intercostal short-cells absent or very rare. Intercostal silica bodies absent. Prickles abundant in B. curtipendula. Crown cells absent. Costal short-cells predominantly paired, or neither distinctly grouped into long rows nor predominantly paired. 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; biochemical type PCK to NAD–ME, or NAD–ME (i.e. B. curtipendula is seemingly an NAD-ME/PCK intermediate while B. gracilis is NAD-ME); XyMS+. PCR sheath outlines even. PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially. PCR sheath extensions absent. PCR cells without a suberised lamella. PCR cell chloroplasts ovoid, or elongated; with well developed grana; centrifugal/peripheral, or centripetal. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells (linked with the bulliforms). Leaf blade ‘nodular’ in section (low ribs); with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (these contributing to the colourless columns). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the large bundles); forming ‘figures’ (anchors, in some large bundles). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Phytochemistry. Tissues of the culm bases with abundant starch. Leaf blade chlorophyll a:b ratio 3.13–4.3.

Cytology. Chromosome base number, x = 10. 2n = 20, 40, 41, 42, 56, 60, 70, and 98. Nucleoli persistent.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Boutelouinae. 40 species.

Distribution, phytogeography, ecology. Canada to South America, especially southwest U.S.A.

Species of open habitats. Dry plains and hillsides.

Economic aspects. Significant weed species: B. aristidoides, B. barbata, B. gracilis. Cultivated fodder: B. curtipendula etc. (Grama grasses). Important native pasture species: B. curtipendula, B. gracilis, B. hirsuta.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia cacabata, Puccinia boutelouae, and Puccinia chloridis. Smuts from Ustilaginaceae. Ustilaginaceae — Ustilago.

References, etc. Morphological/taxonomic: Griffiths 1912; Gould 1979a. Leaf anatomical: Metcalfe 1960; studied by us - B. curtipendula (Michx.) Torr.

Illustrations. • B. curtipendula: Griffiths, Cont. U.S. Nat. Herb. 14 (1912). • Spikelet clusters of B. curtipendula. • Spikelet clusters of B. curtipendula. • B. hirsuta (Chondrosum): General aspect. • B. scorpioides (Chondrosum): Griffiths, Cont. U.S. Nat. Herb. 14 (1912). • B. gracilis (Chondrosum): Griffiths, Cont. U.S. Nat. Herb. 14 (1912). • Inflorescence of B. gracilis. • B. gracilis, T.S. of leaf blade (fluorescence image): this project. • Pollen antigens: Watson and Knox (1976)

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: 11th December 2017.’.