Chusquea enigmatica Ruiz-Sanchez, Mejía-Saulés & L. G. Clark, 2014

Ruiz-Sanchez, Eduardo, Mejía-Saulés, Teresa & Clark, Lynn G., 2014, A new endangered species of Chusquea (Poaceae: Bambusoideae) from the Acatlán volcano in central Veracruz, Mexico, and keys to the Mexican Chusquea species, Phytotaxa 163 (1), pp. 16-26 : 20-24

Chusquea enigmatica Ruiz-Sanchez, Mejía-Saulés & L. G. Clark , spec. nov., Fig. 1 , Fig. 2 A–F , Fig. 3 B–I

TYPE:— MEXICO. Veracruz: cima del volcán de Acatlán sobre el anillo de la parte sureste, suelo negro, planta estéril, bosque de Fagus grandifolia Ehrhart (1788: 22) con Podocarpus matudae Lundell (1937: 212) , 19°47'48.2'' N, 100°41'42.3'' W, 1960 m elevation, 19 February 2013, E. Ruiz-Sanchez & T. M. Mejía-Saulés 434a (Holotype: XAL!, isotypes: IEB!, ISC!, MEXU!).

Chusquea enigmatica is similar to Chusquea glauca , C. muelleri and C. repens but differs in having leptomorph rhizomes, delicate small culms, erect habit and an intravaginal or extravaginal branching pattern.

Rhizomes leptomorph to 40 cm long. Culms 0.2–1.0 cm tall, 0.5–1.5 mm in basal diameter, erect, decumbent and geniculate. Internodes 1–3.5 cm long, 12–15 per culm, terete, glabrous, green, solid. Culm leaves 2.3–4.8 cm long, glabrous, straw-colored, deciduous as branches develop; sheaths 1.8–3.9 cm long, rectangular with rounded shoulders, 4–6 times as long as the blade, the margins entire or ciliate on both sides, glabrous; blades 3–9 mm long, narrowly triangular, erect, deciduous, apex acuminate, margins entire or slightly ciliate, glabrous; girdle not developed, inner ligule 0.2–0.5 mm long, glabrous, truncate. Nodes at mid culm with 1–3 buds, composed of one larger triangular central bud subtended by 1–2 slightly smaller triangular, closely adjacent subsidiary buds arranged in a single line; nodal line horizontal, supranodal ridge present and prominent. Branching extravaginal or intravaginal, the sheaths deciduous, 1–3 branches per node, diverging from the main culm at 45 o, 9–15 cm long, 1– 1.5 mm in diameter, some rebranching. Foliage leaves (5)6–9(11) per complement; sheaths glabrous, the summit short ciliate; leaf blades 10–11.7 cm long, 0.8–1.2 cm wide, L: W = 8–14, abaxially glaucous and adaxially green, glabrous, not tessellate, the base oblique, the apex apiculate, the margin finely serrulate on both sides; pseudopetioles 1–1.5 mm long, adaxially and abaxially glabrous, inner ligule 2–3 mm, rounded; outer ligule to 0.2–0.3 mm long, glabrous or finely ciliate. Synflorescences not seen.

Habitat and distribution:—This species is only known from one population at the summit of the volcano Acatlán ( Fig. 3A ). This volcano is part of the easternmost portion of the Trans-Mexican Volcanic Belt in central Veracruz ( Gómez-Tuena et al. 2007, Ferrari et al. 2012). Chusquea enigmatica inhabits bosque mesófilo de montaña ( Rzedowski 1978) or Neotropical cloud forest ( Webster 1995) dominated by Fagus grandifolia inside of the crater and codominant stands at the rim and top of the same volcano ( Williams-Linera et al. 2000). The mean temperature is 15.2 o C, and total mean annual precipitation is 1532 mm, with three seasons described: dry cold (October-March); dry warm (April–May) and wet warm (June–September). Humidity is high and fog is frequent during most days of the year ( Williams-Linera et al. 2000).

Comparison:—At first glance C. enigmatica looks like an herbaceous bamboo in the forest understory; it is the presence of multiple buds per node that places it in Chusquea . The first collection of this plant was made in 2010 and the plants looked like seedlings. After three years collecting the species several times in the same place and during different seasons, it is observed that the size of the plants did not change. However, individual observations of plants growing in a clearing, exposed to direct sunlight, revealed that this group of plants registered the highest growth, reaching one meter tall. Further observation suggested some similarities to C. glauca , an endemic species of Chusquea sect. Serpentes occurring on the slopes of the Cofre de Perote volcano in central Veracruz, Mexico. Chusquea enigmatica can be distinguished from C. glauca by several characters such as delicate culms 0.2–1.0 m tall and 0.5–2 mm in diameter (vs. 5–6 m, to 1 cm), erect culms (vs. scandent), an extravaginal or intravaginal branching pattern (vs. infravaginal), and foliage leaf blades 10–11.7 cm long and 0.8–1.2 cm wide (vs. 14.4–29 cm, 2.1–4 cm). There are two other small Mexican Chusquea species from section Longifoliae, C. muelleri and C. repens , that could be regarded as similar to C. enigmatica , but there are several characters to differentiate them from it. Chusquea enigmatica has thin culms 0.5–2 mm wide (vs. 5–7 mm wide), one main and two subsidiary buds (vs. one main and several subsidiary buds), and an extravaginal or intravaginal branching pattern (vs. infravaginal).

Etymology:—The specific epithet refers to the unusual morphology with leptomorph rhizomes and reduction in bud and culm sizes and the consequent difficulty in classifying this species within one of the known sections of Chusquea .

Phenology:—Synflorescences and flowers of this species are unknown, but the plants are under cultivation in the National Bamboo Collection at the Francisco Clavijero Botanic Garden in Xalapa, Veracruz.

Additional specimens examined:— MEXICO. Veracruz: cima del volcán de Acatlán sobre el anillo de la parte sureste, suelo negro, planta estéril, bosque de Fagus grandifolia con Podocarpus matudae , 19°47'48.2'' N, 100°41'42.3'' W, 1960 m elevation, 28 June 2010, E. Ruiz-Sanchez & J. F. Ornelas 299 (XAL); 17 August 2013, E. Ruiz-Sanchez & L. G. Clark 460 (XAL).

Figures

FIGURE 1. Chusquea enigmatica. Complete plant with leptomorph rhizomes (right, vertical orientation). Based on E. Ruiz-Sanchez & T.M. Mejía-Saulés 434a. Drawn by Edmundo Saavedra.

FIGURE 2. Chusquea enigmatica. A. Part of leptomorph rhizome, shown with vertical orientation. B. Culm fragment showing intravaginal branch pattern and culm leaves. C. Culm fragment showing extravaginal branch pattern, complete culm leaves with erect blade and development of a new branch. D. Nodal section of the culm, showing bud complement, with one main central bud and two subsidiary smaller buds. E. Culm fragment, showing two nodal regions with well development branches. F. Foliage leaf complement, showing inner ligule and finely serrulate margins. Based on E. Ruiz-Sanchez & T.M. Mejía-Saulés 434a. Drawn by Edmundo Saavedra.

FIGURE 3. Habitat and plants of Chusquea enigmatica. A. Acatlán volcano, black arrow indicates the location of C. enigmatica in Fagus grandifolia dominated Neotropical cloud forests. B. Plants of C. enigmatica in the understory of Fagus grandifolia. C. Small patch of C. enigmatica showing erect habit. D. Foliage leaf complement abaxial view, showing six foliage leaves. E. Leptomorph rhizome. F. Bud complement, showing one triangular central bud and two smaller subsidiary buds. G. Branches, showing three branches per node. H. Extravaginal branch pattern. I. Culm leaves and intravaginal branch pattern. Clb = culm leaf erect blade, Ibp = intravaginal branch pattern. Photos by E. Ruiz-Sanchez.