15. Muhlenbergia minutissima (Steud.) Swallen, Contr. U.S. Natl. Herb. 29(4):207. 1947.

Fig. 12E-H

Agrostis minutissima Steud., Syn. PI. Glumac. 1:171. 1854 Type: U.S.A., New México, 1847, A. Fendler 986 (holotype: not located; isotypes: F-72158 [image!], MO!, NY-327637!, S-29780 [image!], US-825378!, US-997292!, W-0030511 [image!]). ≡ Sporobolus minutissimus (Steud.) Hitchc, Proc. Biol. Soc. Wash. 41:161. 1928. Basionym.

= Milium microspermum Lag., Gen. Sp. PI. 2. 1816, Type:: México, Habitat in Nova Hispania, D. Sesse s.n. (holotype: MA; isotype: US-91019! fragm.). non Muhlenbergia microsperma (DC.) Trin. 1824. ≡ Panicum microspermum (Lag.) E. Fourn., Mexic. Pl 2: 492. 1886. ≡ Sporobolus microspermus (Lag.) Hitchc, J. Wash. Acad. Sci. 23(10):453. 1933.

= Vilfa confusa E. Fourn., Mexic. PL 2: 101. 1886. Type: México, Jalicingo, C.].W. Schiede & Deppe 913 (syntype: US-998282! fragm. ex P); Orizaba, Botteri 117 (syntypes: P!, US! fragm.); Orizaba, Schaffner 93 (syntypes: P!, US! fragm. ex P); Orizaba, Schajfner 125 (syntype: P!); Nevado de Toluca, Sep, Hahn s.n. (syntype:: P!); U.S.A., Hall & Harbour 643 (syntype: P!). ≡ Sporobolus confusus (E. Fourn.) Vasey, Bull. Torrey Bot. Club 15:293. 1888. ≡ Muhlenbergia confusa (E. Fourn.) Swallen, Contr. U.S. Natl. Herb. 29(4): 207. 1947.

Description.

Delicate annuals. Culms 5-40 cm tall, erect or spreading, slender, scaberulous to strigulose below the nodes, 0.3-0.7 mm diameter just below the inflorescence; internodes 8-25 mm long. Leaf sheaths 4-52 mm long, shorter to longer than the internodes, glabrous or scaberulous, margins hyaline; ligules 1-2.6 mm long, hyaline, apex irregularly toothed to lacerate, truncate to obtuse, margins entire, sometimes splitting off to form auricles which are not longer than the body of the ligule; blades 0.5-4.0(-10) cm long, 0.8-2.0 mm wide, flat or involute, short pubescent above and scabrous below. Panicles 5.0-16.2(-21) cm long, 1.5-6.5 cm wide, open, ovate, nodes 12-35 per inflorescence; primary branches 8-42 mm long, one or two per node, spreading 25-80° from the rachis; pedicels 2-7 mm long, slender often capillary, erect. Spikelets 0.8-1.5 mm long, erect; glumes 0.5-0.9 mm long, subequal, 1-veined, sparsely short-pilose at least near apex; lower glumes 0.5-0.8 mm long, obtuse to acute; upper glumes 0.6-0.9 mm long, obtuse, usually broader than the first glume; lemmas 0.8-1.5 mm long, lanceolate, with short appressed silky pubescence located along the midvein and margins to glabrous, unawned, apex obtuse to subacute; paleas 0.8-1.4 mm long, about as long as lemma, with short appressed silky pubescence between the veins or glabrous; anthers 0.2-0.7 mm long, purplish. Caryopses 0.6-0.9 mm long, fusiform to elliptic, brownish. 2 n = 60, 80.

Distribution.

Western North America from central Washington to Montana south to Texas, U.S.A. and throughout México to Guatemala (Peterson and Annable 1991).

Ecology.

Sandy and gravelly drainages, rocky slopes, flats, road cuts, and open sites most commonly in yellow pine forests, oak-pine forests with Arctostaphylos, thorn scrub forests with Acacia, pinyon-juniper woodlands, and oak-gramma grass ( Bouteloua) savannahs; 1200-3000 m.

Comments.

Morphologically, Muhlenbergia minutissima can be separated from other annual species of Muhlenbergia in Central America in having sparsely short-pilose glumes near the apex and open, ovate, panicles with pedicels that are longer than the spikelets (2-7 mm long [Peterson and Annable 1991].

Based on DNA sequence analysis, Muhlenbergia minutissima is a member of M. subg. Bealia and shares a most recent common ancestor with M. sinuosa Swallen, a species known to occur in Arizona and New Mexico, USA and Chihuahua and Sonora, México (Peterson and Annable 1991; Peterson et al. 2021).

Specimens examined.

Guatemala. Quetzaltenango: Santa Maria, Volcano Agua, A.S. Hitchcock 9130 (MICH, US-998503) . Quiché: W.A. Archer 3858 (US-1646054) . Totonicapán: E of San Cristóbal Totonicapán, Harmon 4570 (ENCB, NY) .