Podagrostis exserta (Swallen) Sylvester & Soreng, 2020

Sylvester, Steven P., Peterson, Paul M., Romaschenko, Konstantin, Bravo-Pedraza, William J., Cuta-Alarcon, Lia E. & Soreng, Robert J., 2020, New combinations and updated descriptions in Podagrostis (Agrostidinae, Poaceae) from the Neotropics and Mexico, PhytoKeys 148, pp. 21-50 : 21

Podagrostis exserta (Swallen) Sylvester & Soreng comb. nov. Fig. 2

Agrostis exserta Swallen, Contr. U.S. Natl. Herb. 29(9): 404. 1950.

Type.

Guatemala. Dept. Huehuetenango: collected in alpine area, vicinity of Tojquia, Sierra de los Cuchumatanes, 3700 m alt., 5 Aug. 1942, J.A. Steyermark 50119 (holotype: US (US00131747 [not seen]); isotype: US (US00131748 [not seen])).

Description.

Tufted perennial forming short dense tufts, with the basal mats reaching c. 3-6 cm tall and inflorescences usually well-exserted from the basal foliage. Tillers intravaginal. Culms 5-15(-30) cm tall, erect, simple, delicate; nodes and internodes terete, smooth, nodes usually hidden in the sheaths with 0(-1) nodes exposed at flowering, uppermost internode usually <1 cm long (to 4 cm long in Steyermark 50216), usually not longer than the sheath. Leaves generally basal; sheaths terete, glabrous, smooth; flag sheath 2-5.6 cm long; basal sheaths 0.5-1.5 cm long, striate, becoming fibrous; ligules 0.8-2(-2.5) mm long, membranaceous, slightly to usually strongly decurrent with the sheath; upper culm ligules acute with a obtuse to truncate apex, usually slightly erose towards the apex; ligules of tillers similar to those of the culm; blades 1-4(-5.5) cm long, 0.3-0.4(-0.6) mm wide in diameter, involute or convolute, acicular to capillaceous and filiform, usually curved, abaxial surfaces glabrous, smooth, adaxial surfaces glabrous, lightly to usually densely scabrous with scabers usually short, less often long and robust, edges smooth to lightly scabrous with very short hooks. Panicles (1.2-)2-5 × (0.5-)1-2.5 cm, open to slightly congested when young, usually ovoid; panicle branches ascendant to patent, branched above the middle, filiform, with spikelets not present near the base, glabrous, smooth, longest branches 0.3-2 cm long; pedicels (1-)1.5-5 mm long, usually longer than the length of the spikelets, divaricate, glabrous, smooth. Spikelets (1.2-)1.5-2 mm long; glumes remaining on the inflorescence at maturity, equal or subequal, the lower usually slightly longer than the upper, subequaling the length of the floret or slightly longer, oblong-lanceolate, slightly keeled, apex broadly acute, glabrous, keels lightly scaberulous just in the distal 1/3, surfaces smooth; lower glume 1- or 3-veined; upper glume 1- or 3-veined; lemmas (1.1-)1.4-1.6 mm long, glabrous, smooth, faintly to strongly 5-veined, apex obtuse, awn lacking or to 0.5 mm long, straight, inserted medially or in the upper 1/3; paleas 0.9-1.3 mm long, notable, usually reaching from ¾ to subequaling the lemma, infrequently reaching 2/3 the length of the lemma, keels usually obscure, smooth, apex bifid and erose; rachilla 0.3-0.5 mm long, prolonged from the base of the floret (sometimes lacking in a small number of spikelets within the inflorescence), glabrous, smooth or scabrous. Calluses 0.1-0.2 mm long, slightly elongated, glabrous, smooth. Flowers; lodicules c. 0.5 mm long, lanceolate with acute apices, not lobed; anthers 3 in number, 0.7-1.1 mm long. Caryopses not seen. 2 n = unknown.

Distribution and ecology.

Guatemala, endemic. Grows in alpine grasslands on volcanic soils, 2900-3700 m.

Additional specimens examined.

Guatemala. Huehuetenango: Sierra de los Cuchumatanes, alpine areas in vicinity of Tunima, 3400-3500 m alt., 7 July 1942, J.A. Steyermark 48321 (US1914763; US2208640); Sierra de los Cuchumatanes, between Tojiah and Chemal at km 319.5 on Ruta Nacional 9N, 3380 m alt., 31 July 1960, J.H. Beaman 3873 (US01247246); Sierra de los Cuchumatanes, between Tojquia and Caxin bluff, summit of Sierra de los Cuchumatanes, 3700 m alt., 6 Aug. 1942, J.A. Steyermark 50216 (US2181354). Solola: Woods 11 miles SE of Totonicapan, 3200 m alt., 27 June 1962, G.L. Webster 11826 (US3336153). Totonicapan: Desconsuelo, potrero natual, 3100 m alt., Aug. 1954, M. de Koninck 201 (US2153266); On the Tecum Uman Ridge at km 154 on Ruta Nacional No. 1, ca. 20km east of Totonicapan, 3340 m alt., 13 Aug. 1960, J.H. Beaman 4154 (US2381726).

Notes.

Similar in general habit to P. trichodes (see notes under this species for how to distinguish them). Podagrostis bacillata also has smooth panicle branches and pedicels and bears very similar spikelet characteristics to P. exserta , with both having spikelets usually measuring> 1.5 mm long, with smooth glumes apart from the keel being lightly scaberulous, and smooth lemmas. Podagrostis bacillata can be distinguished from P. exserta principally by the culms having at least one visible elongated internode, 4-13 cm long, with usually at least one node exserted from the sheaths (vs. usually no visible elongated internodes or nodes, with the distalmost internode usually <1 cm long in P. exserta ), leaf blade abaxial surface lightly to usually densely scabrous (vs. smooth in P. exserta ), leaf blades usually longer, 2-15 cm long, forming a basal mat reaching c. 6-17 cm tall (vs. usually <4 cm long, forming a basal mat reaching c. 3-6 cm tall in P. exserta ), ligules 1.7-4.3 mm long (vs. 0.8-2.5 mm long in P. exserta ), and a rachilla prolongation 0.3-1.4 mm long (vs. 0.3-0.5 mm long in P. exserta ), (also see notes under P. bacillata ). However, one specimen (Steyermark 50216) did have a moderately long internode at c. 4 cm long, as well as slightly longer leaf blades to 5.5 cm long, but could be differentiated based on the short ligules, <1.4 mm long, short panicles <3 cm long, and, crucially, the leaf blade abaxial surface being smooth, with scabers only present on the adaxial surface.

The possible affinity of A. exserta to Podagrostis was mentioned previously ( Pohl and Davidse 1994; Briceño 2010), with Pohl and Davidse (1994) recommending transfer of A. exserta to Podagrostis . Despite repeated efforts by different researchers (e.g. P. Barbera, Y. Herrera, P.M. Peterson, J. R Reichman, K. Romaschenko, L.S. Watrud, pers. comm.) to sequence leaf samples from herbarium specimens of this species, none have been successful to date largely due to the available specimens having mostly aged, brownish leaves. This may be a characteristic of the species in general, with only new fresh shoots being found very early in the growing season and becoming brown at maturity. Successful molecular sampling of this species is necessary.

Figures

Figure 2. Podagrostis exserta. A Whole plant B Spikelets, the upper glume of the left-hand spikelet has been removed to reveal the rachilla prolongation (indicated with a red arrow) C leaf blade adaxial view, showing scabers on the adaxial surface and smooth abaxial surface of the leaf blade. A Digitized image of specimen J. H. Beaman 3873 (US 01247246) courtesy of United States National Herbarium (US) B, C images of specimen G. L. Webster 11826 (US 3336153).