Muhlenbergia tenuissima (J. Presl) Kunth, Enum. Pl. 1:198 (1833).

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

33. Muhlenbergia tenuissima (J. Presl) Kunth, Enum. Pl. 1:198 (1833).

Fig. 19E-H

Podosemum tenuissimum Presl, Rel. Haenk. 1: 230. 1830. Type: Panama or México. Haenke s.n. (lectotype, designated here: PRC-450957 [image!]; isolectotypes: MO-2974335!, US-91923!, W-0002565!, W-0002566!, W-239298!). Basionym:

= Muhlenbergia nebulosa Scribn. ex Beal, Grasses N. Amer. 2: 247. 1896. Type: México, Jalisco, wet places, hills near Guadalajra, 5 Nov 1889, C.G. Pringle 2366 (holotype: MSC-11271!; isotypes: BR-0000006883102 [image!], BR-0000006883430 [image!], E-00373720 [image!], F-73212 [image!], GH!, GOET-006642 [image!], IBUG-0179259 [image!], K!, KFTA-0000118 [image!], LL-00370119 [image!], MEXU-00005184 [image!], MEXU-00005183 [image!], UC-122478 [image!], NY!, RSA!, S-G-4200 [image!], SI-002778 [image!], US!, VT!, W-1916-29044!, W-1890-597!).

Description.

Delicate, slender, annuals. Culms 5-30(-38) cm tall, much branched near base and above often sprawling, glabrous or scaberulous below the nodes; 0.1-0.2 mm diameter just below the inflorescence; internodes 7-30 mm long. Leaf sheaths 4-20 mm long, glabrous or scaberulous, shorter than the internodes; margins membranous; ligules 0.6-1.5 mm long, membranous, thin, apex rounded to acute, sometimes lacerate; blades 1-5 cm long, 0.6-1.4 mm wide, flat or loosely involute, short pubescent above and glabrous to scaberulous below, margins and abaxial midvein often whitish-thickened. Panicles 6-16 cm long, 1.0-2.5(-6.0) cm wide, open, few-flowered with 9-16 nodes; panicle branches 0.5-4.0 cm long with ascending and spreading branches up to 70° from the culm axis; pedicels 1-4 mm long, scabrous, erect, ascending. Spikelets 1.3-1.9 mm long; glumes 0.4-0.8 mm long, subequal, subacute, mostly glabrous, 1-veined, minutely scabrous along veins and near apex; lower glumes 0.4-0.7 mm long, apex sometimes apiculate; upper glumes 0.6-0.8 mm long, apex sometimes mucronate, the mucro up to 0.2 mm long; lemmas 1.3-1.8 mm long, lanceolate, very thin, awned, pilose along the margins and midvein, the hairs up to 0.3 mm long, the awn 3-9 mm long, scabrous, mostly straight; callus short pilose; paleas 1.3-1.9 mm long, as long or slightly longer than the lemma, narrow lanceolate, loosely pilose between the two veins on the proximal 2/3; anthers 0.5-0.6 mm long, purplish or pale. Caryopses 0.8-1.1 mm long, fusiform, light reddish-brown.

Distribution.

Muhlenbergia tenuissima ranges from México in Chiapas, Colima, Jalisco, Nayarit, and has been reported in Sonora and Sinaloa ( Dávila et al. 2018; Sanchez-Ken 2018). It also extends into Costa Rica, Honduras, Nicaragua, and Panama.

Ecology.

This species occurs in tropical forests, savannah grasslands with Quercus and Acacia often in calcareous derived soils in wet soils, moist depressions, and ephemeral moist flats; 50-1900 m.

Comments.

This distinctive species is under collected and confused with other ephemeral annuals. Distinguishing features include lemmas 1.3-1.8 mm long, pilose margins and midvein, apical awns 3-9 mm long, and short anthers 0.5-0.6 mm long ( Peterson and Annable 1991).

Muhlenbergia tenuissima is a member of M. subg. Pseudosporobolus where it is found to be sister to M. wrightii Vasey ex J.M. Coult., although the branches that unite these species are long suggesting a moderate amount of genetic divergence ( Peterson et al. 2021).

Specimens examined.

Costa Rica. Guanacaste: 5 km S of Liberia along the Carretera Interamericana, R.W. Pohl & G. Davidse 11554 (US); 2 km E of carretera Interamericana on road to Las Animas, R.W. Pohl & G. Davidse 11530 (CR, UD). Honduras. Comayagua: vicinity of Siguatepeque, P.C. Standley 55871 (US). Morazán: Las Mesas, J.V. Rodriguez 3683 (US). Olancho: tree infested savanna called Sav. Amate, ca. 14 km NE of Catacamas, C.L. Johannessen 964 (US). Yoro : Savanna of Puentecita ca. 8 km N of Yoro, C. L. Johannessen 707 (US). Mexico. Chiapas: Ixtapa: near Ixtapa, D.E. Breedlove & G. Davidse 54331 (CAS, MO). Nicaragua. Chontales: Quebrada Niscala, ca. 2.3 km SE of bridge over Quebrada Niscala along road between Acoyapa and Río Oyate; savanna, D.W. Stevens 19067 (MO). Panama. Panamá: Panama City, along road between Panamá and Chepo, C.W. Dodge et al. 16687 (MO); Juan Diaz, M. A. Cornman 625 (US); E.P. Killip 4214 (ARIZ); Agricultural Experiment Station at Matías Hernandez, H. Pittier 6918 (US); Meadows, Sabana of Panama, Canal Zone, H. Pittuer 2544 (US); Rio Tecumen, P.C. Standley 29418 (US); along road between Panama and Chepu, C.W. Dodge 16687 (US) .

Figures

Figure 19. A-D Muhlenbergia ramulosa (Kunth) Swallen A habit B floret C glumes D ligule E-H Muhlenbergia tenuissima (J. Presl) Kunth E habit F floret G glumes H ligule. A drawn from P. M. Peterson & C. R. Annable 5602 (US- 3182911) B-D drawn from P. M. Peterson & C. R. Annable 4661 (US, WS) E-H drawn from P. M. Peterson & C. R. Annable 4751 (US, WS).