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The grass genera of the world

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

Pereilema J. & C. Presl

~ Muhlenbergia sensu lato

Habit, vegetative morphology. Annual; caespitose. Culms 30–60 cm high; herbaceous; unbranched above. Culm nodes glabrous. Plants unarmed. Leaves not basally aggregated; auriculate. Leaf blades narrow; 2–5 mm wide; flat; without abaxial multicellular glands; without cross venation; persistent. Ligule an unfringed membrane; 0.5 mm long. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and sterile, or hermaphrodite, male-only, and sterile; overtly heteromorphic (in bunches, some of each group bisexual and the rest incomplete or ‘reduced to glumes or bristles’).

Inflorescence. Inflorescence of spicate main branches to a false spike, with spikelets on contracted axes (the spikelet clusters being subsessile on appressed spike-like laterals, which decrease in length towards the tip of the main axis - cf. Sporobolus, apart from the awns); contracted (plumose by the long lemma awns). Primary inflorescence branches 16–25 (or more). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes very much reduced, or ‘racemes’; disarticulating (P. ciliatum), or persistent; falling entire (the main branches falling, in P. ciliatum). Spikelets with ‘involucres’ of ‘bristles’ (representing reduced spikelets - the ‘involucre’ to one side). The ‘bristles’ deciduous with the spikelets. Spikelets secund (the clusters one-sided).

Female-fertile spikelets. Spikelets morphologically ‘conventional’ (when the spikelet cluster is dissected out); 2 mm long (to 3 cm with the awns); compressed laterally; disarticulating above the glumes (when the inflorescence branches fall entire, the florets also disarticulate). Rachilla terminated by a female-fertile floret. Hairy callus present.

Glumes two; more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; when not reduced to bristles, hairless (the keel scabrid); awned (the awns long, straight, scabrid); carinate; similar (hyaline, emarginate, or sometimes reduced to ciliate bristles in P. ciliatum). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.

Female-fertile florets 1. Lemmas similar in texture to the glumes to decidedly firmer than the glumes (becoming hardened in the fruit); not deeply cleft; mucronate to awned. Awns 1; median; apical; non-geniculate; hairless (scabrid, slender); usually much longer than the body of the lemma (to 3 cm long); persistent. Lemmas hairless; scabrous; carinate; without a germination flap; 3 nerved. Palea present; relatively long; apically notched; awnless, without apical setae to with apical setae (the nerves slightly excurrent); not indurated (hyaline); 2-nerved; 2-keeled. Lodicules absent. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit ellipsoid. Pericarp fused. 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 present; intercostal. Intercostal papillae several per cell. Long-cells intercostal long-cells very thin-walled. Mid-intercostal long-cells having straight or only gently undulating walls. Microhairs present; elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs (24–)25.5–27(–30) microns long. Microhair basal cells 9–12 microns long. Microhairs 10.5–12 microns wide at the septum. Microhair total length/width at septum 2.1–2.6. Microhair apical cells 6–9 microns long. Microhair apical cell/total length ratio 0.22–0.35. Stomata common; 19–24 microns long. Subsidiaries parallel-sided and dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal silica bodies absent. Prickles abundant. Costal silica bodies present in alternate cell files of the costal zones; ‘panicoid-type’; 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. Mesophyll traversed by columns of colourless mesophyll cells. Leaf blade ‘nodular’ in section. Midrib conspicuous; having a conventional arc of bundles (the large median flanked by a small lateral on each side); with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups (in addition to large ‘midrib hinges’); associated with colourless mesophyll cells to form deeply-penetrating fans (these incorporated in the wide colourless girders). All the vascular bundles accompanied by sclerenchyma. Sclerenchyma all associated with vascular bundles.

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

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Muhlenbergiinae (as a synonym of Muhlenbergia). 3 species.

Distribution, phytogeography, ecology. Mexico to tropical South America.

Species of open habitats. Hills and weedy places in savanna.

Rusts and smuts. Rusts — Puccinia.

References, etc. Leaf anatomical: this project.

Special comments. Fruit data wanting. Illustrations. • P. beyrichianum, as Muhlenbergia: Kunth (1835), Dist. méthodique de la famille Graminées


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: 13th November 2017. delta-intkey.com/grass’.

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