Muhlenbergia quadridentata (Kunth) Trin., Gram. Unifl. Sesquifl. 194, t. 5b, f. 14. 1824.

Peterson, Paul M., Herrera Arrieta, Yolanda, Lobo Cabezas, Silvia & Romaschenko, Konstantin, 2023, Taxonomic revision of Muhlenbergia (Poaceae, Chloridoideae, Cynodonteae, Muhlenbergiinae) in Central America: phylogeny and classification, PhytoKeys 230, pp. 1-106 : 1

26. Muhlenbergia quadridentata (Kunth) Trin., Gram. Unifl. Sesquifl. 194, t. 5b, f. 14. 1824.

Fig. 15A-E

Podosemum quadridentatum Kunth, Nov. Gen. Sp. (quarto ed.) 1:130-131. 1816. Type: México, México, near Toluca, Sep, F.W.H.A. Humboldt & A.J.A. Bonpland s.n. (lectotype: P-BONPL!, designated by McVaugh p. 253. 1983; isolectotypes: GH, US-2557456!, US-86634 fragm. ex P!, US-86635!). ≡ Agrostis quadridata (Kunth) Spreng., Syst. Veg. [Sprengel] 1: 263. 1825 (1824). ≡ Muhlenbergia quadridentata (Kunth) Kunth, Révis. Gramin. 1:64. 1829, isonym. ≡ Trichochloa quadridentata (Kunth) Roem. & Schult., Syst. Veg. 2:388. 1817. ≡ Muhlenbergia virescens subsp. quadridentata (Kunth) Y. Herrera, Amer. J. Bot. 81(8):1043. 1994. Basionym.

= Podosemum gracile Kunth, Nov. Gen. Sp. (quarto ed.) 1:131-132. 1816. Type: México, Michoacán, Volcán de Jorullo, Sep, F.W.H.A. Humboldt & A.J.A. Bonpland s.n. (holotype: P-BONPL!; isotypes: LE-TRIN-1501.02!, US-86636 fragm. ex P-BONPL!). ≡ Muhlenbergia gracilis (Kunth) Trin., Gram. Unifl. Sesquifl. 193, t. 5a, f. 6. 1824. ≡ Trichochloa gracilis (Kunth) Roem. & Schult., Syst. Veg. (ed. 15 bis) 2: 389. 1817. ≡ Muhlenbergia gracilis (Kunth) Kunth, Révis. Gramin. 1:64. 1829, isonym.

Description.

Caespitose perennials with short, stout rhizomes. Culms 20-70 cm tall, erect, mostly glabrous below the nodes, the nodes basal, flattened, 1 node per culm; internodes mostly scabrous. Leaf sheaths 10-30 cm long, shorter than the internodes, scabrous to smooth; basal sheaths densely pubescent to glabrous abaxially, smooth and shiny adaxially, becoming flattened and usually not spirally twisted with age; ligules 2-8 mm long, membranous to hyaline above, firm and often brownish with evident veins near the margins below, decurrent, apex acuminate often lacerate; blades 5-15 cm long, 0.6-2 mm wide, flat or usually tightly involute, scaberulous below, short-spiculate and often villous above, the hairs 0.2-0.5 mm long, usually appressed, the spicules shiny to whitish. Panicles 5-20 cm long, 0.5-2 cm wide, narrow, loosely-contracted, interrupted below, mostly plumbeous; central axis flattened with 2 ribs, scabrous; primary branches 0.5-5(-6) cm long, appressed and ascending to spreading up to 30° from the rachises; pedicels 0.5-2 mm long, shorter than the spikelets, scabrous. Spikelets 3.4-4.7 mm long, mostly plumbeous; glumes 1.8-4 mm long, shorter to almost as long as the floret, unequal, mostly greenish-plumbeous, scabrous, usually with a few short hairs below; lower glumes 1.8-2.5 (-3) mm long, 1-veined, apex obtuse to acute, often with 2 small teeth; upper glumes (3-)3.2-4 mm long, 3-veined, apex truncate, obtuse or acute, often with 3 or 4 small teeth, the teeth less than 1/6 the length of the glumes; lemmas 3-4.7 mm long, lanceolate, terete, usually awned, greenish-plumbeous to mottled-plumbeous, sparsely pilose near base and margins on lower ½, apex acuminate, scabrous, the awns 1-20 mm long, flexuous, scabrous, greenish-plumbeous; paleas 2.8-4.3 mm long, shorter than the lemma, pilose on the proximal ½; anthers 1-2.5 mm long, purple. Caryopses 1.8-2 mm long, fusiform, brownish. 2 n = 20.

Distribution.

This species is found throughout México in the higher mountains extending to Guatemala ( Peterson et al. 2001).

Ecology.

Muhlenbergia quadridentata occurs on open to forested slopes derived from calcareous and volcanic rocks, and is associated with Pinus ssp., Abies sp., Holodiscus discolor (Pursh) Maxim., Populus tremuloides Michx., Pseudostuga , and Quercus ssp.; (1900-) 2500-4100 m.

Comments.

The distinction between M. quadridentata and M. virescens (Kunth) Kunth is minimal and it has been suggested that quite possibly they represent different morphological forms of a single species corresponding to different habitats ( McVaugh 1983). Generally, the plumbeous spikeleted forms ( M. quadridentata ) are found above 2500 m whereas the whitish-hyaline to grayish-green forms ( M. virescens ) are found between 1600-2700 m. Even this color distinction can break down since intermediate individuals are not uncommon. One character that seems to be fairly consistent within each species is the presence of hairs at the base of the glumes. In addition to having dull, scabrous glumes, most individuals of M. quadridentata have a few short hairs near the base, whereas individuals of M. virescens have whitish or stramineous glumes that are glabrous and shiny near the base. Usually the upper glume apices of M. quadridentata are truncate with 3 or 4 teeth whereas the glume apices of M. virescens are acute and entire (Herrera Arrieta and Peterson 2018).

Muhlenbergia quadridentata is a member of M. subg. Clomena and it pairs with M. flabellata in a recent DNA molecular sequence analysis ( Peterson et al. 2021). However, M. virescens aligns in a clade with M. montana , M. straminea Hitchc., and M. curvula Swallen [the latter two species treated as synonyms of M. virescens in Herrera Arrieta and Peterson (2018)].

Specimens examined.

Guatemala. Huehuetenango: San Juan Ixcoy, Ul-xemal, M. Véliz 98.689 (MO); Pine-Juniperus woodland near Tojquia, summit of Sierra de los Cuchumatanes, J.A. Steyermark 50229 ( US); Sierra de los Cuchumatanes, between Tojiah and Chemal at km 319.5 on Ruta Nacional 9N, in grassy meadow, J.H. Beaman 3874 ( US). Mexico. Chiapas: Cintalapa: 1 km al E de Rizo de Oro, P. Dávila s.n. (MEXU).

Figures

Figure 15. A-E Muhlenbergia quadridentata (Kunth) Trin. A habit B ligule C glumes D floret E stamens, pistil, and lodicules F-J Muhlenbergia orophila Swallen F habit G ligule H glumes I floret J stamens, pistil, and lodicules. A-E drawn from P. M. Peterson & C. R. Annable 6201 (US) F-J drawn from P. M. Peterson & C. R. Annable 11105 (US).