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

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

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) .

Figures

Figure 12. A-D Muhlenbergia peruviana (P. Beauv.) Steud. A habit B floret C glumes D ligule E-H Muhlenbergia minutissima (Steud.) Swallen E habit F ligule G spikelet H floret. A-D drawn from P. M. Peterson & C. R. Annable 4067 (US, WS) E, G, H drawn from P. M. Peterson & C. R. Annable 5601 (US- 3182908) F drawn from P. M. Peterson & C. R. Annable 4675 (US, WS).