Muhlenbergia microsperma (DC.) Kunth, Revis . Gramin. 1:64. 1829.

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

14. Muhlenbergia microsperma (DC.) Kunth, Revis. Gramin. 1:64. 1829.

Fig. 11A-E

Trichochloa microsperma DC., Cat. Pl. Horti Monsp. 151. 1813. Type: México, cultivated at botanical garden at Montpellier from seeds collected in México and distributed by the Botanical Garden of Madrid, M. Sésse & J.M. Mociño s.n. (holotype: MPU; isotypes: G-00099434 [image!], P!, US fragm. ex P!). ≡ Muhlenbergia microsperma (DC.) Trin., Gram. Unifl. Sesquifl. 193. 1824, nom. inval. Basionym.

= Agrostis microsperma Lag., Gen. Sp. Pl. 2. 1816. Type: México, plants grown at H.R. Matritensis (= Herbario del Real Jardín Botánico de Madrid) from seeds collected by M. Sessé & J.M. Mociño in Nueva Espania, Oct, 1806, M. Sessé & J.M. Mociño s.n. (lectotype, designated here: SEL-H10620 [image!]).

= Podosemum debile Kunth, Nov. Gen. Sp. (quarto ed.) 1: 128. 1816. Type: Ecuador, Prov. Pichincha, Quito, F.W.H.A. Humboldt & A.J.A. Bonpland s.n. (holotype: P-Bonpl!; isotypes: B-W, P!, US-91924 fragm. ex P-Bonpl!). ≡ Trichochloa debilis (Kunth) Roem. & Schult., Syst. Veg. 2:385. 1817. ≡ Muhlenbergia debilis (Kunth) Trin., Gram. Unifl. Sesquifl. 193, t. 5, f. 18. 1824.

= Podosemum setosum Kunth, Nov. Gen. Sp. (quarto ed.) 1:129. 1816. Type: México, between Gueguetoque and Tula, Aug, F.W.H.A. Humboldt & A.J.A. Bonpland 4174 (holotype: P-Bonpl!; isotypes: B-W, US-91917 fragm. ex P-Bonpl!). ≡ Trichochloa setosa (Kunth) Roem. & Schult., Syst. Veg. 2:386. 1817. ≡ Agrostis setosa (Kunth) Spreng., Syst. Veg. 1:262. 1825. ≡ Muhlenbergia setosa (Kunth) Trin., Gram. Unifl. Sesquifl. 193, t. 5, f. 22. 1824. ≡ Muhlenbergia setosa (Kunth) Kunth, Révis. Gramin. 1:63. 1829, isonym.

= Muhlenbergia purpurea Nutt., J. Acad. Nat. Sci. Philadelphia, ser. 2, 1:186. 1848. Type: USA, California, Santa Barbara Co., Santa Barbara and Santa Catalina Island, Gambel s.n. (holotype: K!).

= Muhlenbergia ramosissima Vasey, Bull. Torrey Bot. Club 13(12):231. 1886. Type: México, Chihuahua, SW Chihuahua, Aug-Nov 1885, E. Palmer 158 (lectotype: NY! designated by Hitchcock, N. Amer. Fl. 27:441. 1935, but without indicating the specific specimen; Peterson and Annable, Syst. Bot. Monogr. 31:61. 1991, indicated the specific specimen; isotypes: LE!, MO-2974152!, P!, US-995580!).

Description.

Caespitose annuals, sometimes appearing as short-lived perennials. Culms 10-80 cm tall, often geniculate at the base, slender, often striate, much branched near the base, scaberulous below the nodes; internodes 1.8-8.6 mm long, mostly scaberulous or smooth. Leaf sheaths 2.2-6.6 mm long, commonly shorter than the internodes, glabrous, smooth or scaberulous; ligules 1-2 mm long, membranous to hyaline, decurrent, margins often extended, apex truncate to obtuse; blades 3-8.5(-10) cm long, 1-2.5 mm wide, flat or loosely involute, scabrous below, strigulose above, often deciduous with age. Panicles 6.5-13.5 cm long, 1-6.5 cm wide, open and not densely flowered, often purplish; primary branches 1.6-4 cm long, ascending or diverging up to 80° from the rachises, spikelet-bearing to the base; pedicels 2-6 mm long, appressed to divaricate, antrorsely scabrous. Cleistogamous panicles with 1-3 spikelets present in the axils of the lower sheaths. Spikelets 2.5-5.3 mm long; glumes 0.4-1.3 mm long, exceeded by the florets, 1-veined, obtuse, often minutely erose; lower glumes 0.4-1 mm long; upper glumes 0.6-1.3 mm long; lemmas 2.5-3.8(-5.3) mm long, narrowly lanceolate, mostly smooth, scaberulous distally, hairy on the lower 1/2 of the margins and midveins, the hairs 0.2-0.5 mm long, the callus hairy, apices acuminate, often bidentate, awned, awns 10-30 mm long, straight to flexuous; paleas 2.2-4.8 mm long, narrowly lanceolate, acuminate; anthers 0.3-1.2 mm long, purplish. Caryopses 1.7-2.5 mm long, fusiform, reddish-brown. 2 n = 20, 40, 60.

Distribution.

Muhlenbergia microsperma occurs in Hawaii, southwestern USA, México, Guatemala, Colombia, Venezuela, Ecuador (including the Galapagos Islands), Peru, and Bolivia ( Peterson and Annable 1991).

Ecology.

Rocky slopes, rock outcrops, sandy drainages, cliffs, and disturbed roadsides usually in desert scrub vegetation with Acacia , Aristida adscensionis L., Baccharis , Bombacaceae , Cactaceae , Dodonaea viscosa (L.) Jacq., Fucraea, Heliotropium , Heteropogon contortus (L.) P. Beauv. ex Roem. & Schult., Lantana , Pitcairnia , Prosopis , Puya , Salvia , Schinus molle L., and Schizachyrium ; 1150-3500 m.

Comments.

Muhlenbergia microsperma can sometimes be confused with M. romaschenkoi known only from Peru and differs from it by having cleistogamous panicles in the axils of the lower sheaths and shorter, obtuse glumes, 0.4-1.3 mm long (glumes acute to acuminate, 2-2.8 mm long in M. romaschenkoi ) [ Peterson et al. 2018].

In a molecular DNA sequence study, M. microsperma forms a strongly supported clade with two other annuals, M. appressa C.O. Goodd. and M. brandegei C.G. Reeder, all members of M. subg. Muhlenbergia (Fig. 1 ; Peterson et al. 2010b). In addition, these three species produce cleistogamous spikelets in the axils of the lower culm branches, enclosed by a sheath ( Peterson and Annable 1991). Cleistogamous spikelets appear to have evolved twice within Muhlenbergia , once in M. subg. Muhlenbergia within the M. appressa - M. brandegei - M. microsperma clade and once in M. sect. Pseudosporobolus in M. cuspidata (Torr. ex Hook.) Rydb. ( Morden and Hatch 1984; Peterson et al. 2010b).

Specimens examined.

Guatemala. Sacatepequez: Above Pastores, wet thicket, P.C. Standley 60819 ( US); Volcano Agua, near Antigua, shady bank, A.S. Hitchcock 9130 ( US); Antigua, W.A. Kellerman 7301 ( US).

Figures

Figure 1. A, B Bayesian tree inferred from combined plastid (ndhA intron, rps 16 - trnK, rps 16 intron, rps 3, and rpl 32 - trnL) and ITS sequences. Thick branches indicate posterior probabilities of 0.95 - 1; species in bold occur in Central America; Scale bar: 2 %.

Figure 11. A-E Muhlenbergia microsperma (DC.) Kunth A habit B inflorescence C ligule D glumes E floret F-J Muhlenbergia ligularis (Hack.) Hitchc. F habit G ligule H glumes I floret J stamens and pistil. A-E drawn from P. M. Peterson 4185 (US, WS) F-J drawn from P. M. Peterson, C. R. Annable, S. Laegaard & R. J. Soreng 12684 (US- 3275569).