Merostachys mexicana Ruiz-Sanchez & L. G. Clark, 2018

Ruiz-Sanchez, Eduardo, Clark, Lynn G., Mejía-Saulés, Teresa & Hernández, Francisco Lorea-, 2018, A new species of Merostachys (Poaceae: Bambusoideae: Bambuseae: Arthrostylidiinae) with the northernmost distribution of the genus, Phytotaxa 344 (1), pp. 31-38 : 32-34

Merostachys mexicana Ruiz-Sanchez & L. G. Clark sp. nov. ( Figs. 1–3 )

TYPE:— MEXICO. Tabasco: Huimanguillo, parte alta del cerro Las Flores, al W de Villa de Guadalupe, 17°21’50.4” N, 93°37’59” W, 1010 m, 18 junio 2015 (fl), S. Zamudio, D. Juárez y J. Hernández Rendón 16946 (holotype IBUG!, isotypes ISC!, MEXU!, MO!, US!, XAL!).

Merostachys mexicana is similar to M. latifolia and M. pauciflora , but differs in having two glumes per spikelet, longer upper glumes, and longer lemmas.

Rhizomes pachymorph with necks 5–10 cm long. Culms 6–10 m tall, 1–2 cm in basal diameter, erect then clambering on vegetation; internodes 30.5–43 cm long, hollow, cylindrical, greenish, mottled with green spots, asperous and retrorsely bearded, walls 1.5–2 mm thick, the lacuna occupying>70% of the total diameter; nodes with an infranodal band of sericeous hairs, the band 4–5 mm wide. Culm leaves 25–35.5 cm long, with sericeous hairs at the juncture of the sheath and the node; sheaths 18–24.5 cm long, adaxially glabrous and shiny, abaxially glabrous but pruinose at the base, apex fimbriate, margins apically fimbriate becoming ciliate along the sheath; fimbriae 10–23 mm long, free, straight at the base and sinuous at the apex, whitish; inner ligule 0.8–1 mm long, membranous, ciliate; blades 7–11 cm, scabrous on the adaxial surface, glabrous on the abaxial surface, margins serrulate, bright green on live plants, apex acute. Branch complement with (7–) 10–25 branches, the branches 20–56 cm long, ca. 2 mm in diam., lower nodes not rebranching; nodes prominent, thickened, ring-like, whitish, with an infranodal band of sericeous hairs. Foliage leaves 6–7(–10) per branch; sheaths glabrous, overlapping margin ciliate; auricles absent; outer ligule 0.2 mm long, apex fimbriate; fimbriae 5–10 mm long, not fused, straight to sinuous, whitish; inner ligule 0.2 mm long, membranous, glabrous, minutely ciliate; pseudopetioles 3–4 mm long, brownish, glabrous, straight to twisted; blades 7.5–11.5 (–15.5) × 1.8–2.1 (–2.7) cm, lanceolate to ovate-lanceolate, with a marginal stripe on the abaxial side, both sides glabrous, the base oblique, the apex acuminate, margins serrulate. Inflorescences 5–8 cm long, racemose, pectinate, with 18–26 spikelets per inflorescence; rachis sericeous; pedicels ca. 1 mm long, sericeous. Spikelets 13–15 mm long, solitary, slightly falcate; glumes 2, unequal, puberulous abaxially, margins ciliate; lower glume 3–4 mm long, 1-nerved; upper glume 8–9 mm long, mucronate, 14–16-nerved; lemma 12–14 mm long, 15–17- nerved, abaxially pubescent, margins ciliate; palea 11–13 mm long, 9–10-nerved, abaxially glabrous, awnless, margins entire, the two central nerves keeled and forming a sulcus; sulcus narrow, ciliate towards the apex, tightly clasping the rachilla extension; rachilla extension 9–14 mm long, tipped with a minute rudimentary floret; lodicules 3, 1–1.5 mm long, membranous and apically ciliate; androecium with three stamens, anthers 6 mm long; gynoecium with an elongate ovary, style bifid, stigmas 2, plumose. Caryopsis nucoid, stramineous, 7–8 mm long, mucronate.

Habitat and distribution:— The new species is only known from two populations; the first is the type population located in the state of Tabasco and the second in the El Triunfo national reserve in the state of Chiapas. Merostachys mexicana inhabits montane cloud forest sensu Rzedowski (1978) at elevations of 1000 to 2080 m a.s.l.

Comparison with other species: — On the basis of vegetative morphology and reproductive characters, Merostachys mexicana is most similar to M. pauciflora and M. latifolia . These species are similar in habit, with erect culms that then clamber on other vegetation. However, M. pauciflora has inflorescences consisting of 1 to 8 spikelets with one spikelet per inflorescence node while M. mexicana and M. latifolia have inflorescences consisting of 10 to 30 spikelets, with the spikelets solitary in M. mexicana or solitary or paired in M. latifolia . Merostachys mexicana has two glumes (lower and upper) whereas M. latifolia has only one, lacking the lower glume. The upper glume in M. mexicana is larger (8–9 mm) than in both M. latifolia (1.5–3.5 mm) and M. pauciflora (0.1–2.1 mm). Merostachys mexicana has larger fertile lemmas (12–14 mm) than M. latifolia (9.5–10 mm).

Etymology: — The specific epithet relates to its geographical distribution in Mexico.

Phenology: — All collections except the type are non-flowering; this is the first reproductive collection for this species and thus we cannot infer the flowering cycle. The flowering pattern best matches the category of gregarious flowering type 2 (“flowering wave”) according to Franklin (2004): most of the individuals flowered, but some sterile individuals were observed. Some seedlings were seen growing under the flowering individuals.

Additional specimens examined (paratypes):— MEXICO. Chiapas: Reserva El Triunfo, on muletrack above Santa Rita on the way to the station, Polígono I, 1720 m, 15°41’N, 92°48’ W, 19 January 1993, L. Clark & G. Cortés 1146 ( ISC, MEXU) ; Angel Albino Corzo, campamento El Triunfo bajando por el sendero a Santa Rita, 1750–2066 m, 15°40’56.8’’N, 92°47’41.3’’W, 21 June 2011, T. Mejía-Saulés A. Vázquez & R. Percino 2127, 2128, 2129, 2130 ( XAL) ; Jaltenango, reserva natural El Triunfo 6 hrs de camino al w de Finca Prusia, 1900, 15°40’N, 92°48’W, 15 May 1982, G. Cortés 102 ( MO, US) . Tabasco: Huimanguillo, Villa Guadalupe, atrás de las torres microondas, 17°21.837’N, 93°37.560’W, 1050 m, 6 November 2015 (fl), E. Ruiz-Sanchez, A. Ortiz & F. Lorea 542, 542a ( IBUG) ; Cerro de microondas, 17°21’48’’N, 93°37’33’’W, 1019 m, 18 June 2017, F. Lorea & L. Tlaxcalteco 6161 ( XAL) .

Figures

FIGURE 1. Merostachys mexicana. A. Culm segment showing a culm leaf with its reflexed blade. B. Internode showing two nodes and bud. C. Detail of the apsidate (fan-shaped) early bud development. D. Culm fragment showing the node and hollow culm with thin walls. E. Culm fragment showing flowering branches. F. Foliage leaf complement. G. Inflorescence showing paired spikelets. H. Spikelet lateral view showing the lower and upper glumes and lemma. Drawing by Daniel Barba based on Ruiz-Sanchez et al. 542 (A–D, F) and Zamudio et al. 16946 (E, G and H).

FIGURE 2. Merostachys mexicana.A. Short-necked, pachymorph rhizomes.B. Segment of the culm, showing a culm leaf and its reflexed blade (rb), white fimbriae (f) and hollow culm (hc). C. Internode section showing infra and supranodal bands with sericeous hairs and the pruinose base of the culm leaf sheath. D. Mid-culm section, showing branch complement. Photos by E. Ruiz-Sanchez.

FIGURE 3. Merostachys mexicana. A. New erect shoots, showing culm leaves. B. Foliage leaves. C. Abaxial side of the foliage leaf complement showing the marginal stripe (white arrow). D. Foliage leaf complement showing the fimbriae (white arrow). E. Old inflorescences. F. Remnant new inflorescence showing spikelets and stamen. G. Nucoid caryopsis (white arrow). Photos by E. Ruiz- Sanchez.