Dichanthelium multiglandulosum Sánchez-Ken, 2017

Sánchez-Ken, J. Gabriel, 2017, Dichanthelium multiglandulosum (Paniceae, Panicoideae, Poaceae), a new species from Jalisco, Mexico, and the reestablishment of Panicum transiens as Dichanthelium transiens, Phytotaxa 307 (1), pp. 23-35 : 24-30

Dichanthelium multiglandulosum Sánchez-Ken , sp. nov. ( Fig. 1 ).

“ Panicum multiglandulosum Sánchez-Ken & Dávila in Dávila et al. (1998: 204), nom. nud.”

Type:— MEXICO. Jalisco. Mpio. Talpa de Allende: 3 km adelante de Cuale por la brecha a Talpa de Allende, Bosque de Pinus oocarpa y P. ayacahuite , sobre laderas húmedas, 2100 m, 31 January 1983, F. J. Santana-Michel 1219 (holotype IBUG-40043!, isotypes IBUG-32535!, IEB!).

Plants perennial, 120–140 cm tall, rhizomatous, rhizomes short, scaly, nearly as wide as the culms, apparently not forming a basal rosette, only one phase of growth recognized, culms cane-like, erect, branching above; internodes 10–14, 2.7–5 mm diameter, glabrous, with glandular spots at or near the apex; nodes glabrous to short-pilose upwards. Leaf sheaths shorter than the internodes, usually with glandular spots, the lower ones glabrous, the upper ones short-pilose with rigid hairs becoming glabrous in age, the margins short-pilose with rigid hairs; ligules 0.2–0.3 mm long, membranous, the apex barely provided with minute hair, mostly glabrous and slightly irregular; collar densely short-pilose; leaf blades 16–26 cm × 13–23 mm, the lower ones shorter to almost reduced, lanceolate, flat, ascending, both surfaces glabrous to short-pilose to hirtellous, densely pilose at the base, the margins scabrellous, densely short-pilose at the base, the base rounded to slightly cordate on the uppermost leaves, the apex attenuate, foliar dimorphism lacking. Synflorescence 16–22 × 14–22 cm, open, diffuse, terminal, paniculate, branches alternating, spreading, branchlets spreading; peduncle up to 20 cm long, sparsely short-pilose, with glandular spots; axes somewhat angular, glabrous or sparsely short-pilose toward the base, with glandular spots; axils short-pilose, the upper ones glabrous; pedicels (0.5–)1.5–8(–11) mm long, capillary, spreading, glabrous, with glandular spots. Spikelets 3.5–4.3 × 1.3–1.4 mm, elliptic, acuminate, purple, green-tinged, wrinkled at the base of the glumes, apparently forming a gland; first glume 1.4–2.4 mm long, up to one-half as long as the spikelets, ovate-elliptic, 1-nerved or nerveless, glabrous; second glume 3–4.1 mm long, 9-nerved, the 2 lateral nerves of the midnerve not prominent, nearly wanting, glabrous; lower floret sterile; sterile lemma 3.2–4.2 mm long, 9-nerved, glabrous, similar to the second glume; sterile palea 3–3.5 mm long, 0.5–0.8 mm wide, slightly shorter than the fertile lemma, linear, membranous, 2-keeled, the keels minutely scabrellous, unwinged, puberulent; fertile lemma 3.1–3.8 × 1.3–1.5 mm, elliptic, smooth to slightly rugulose, lustrous, yellowish to stramineous, apex acute, umbonate, usually with some minute antrorse hairs at the apex, 7-nerved but appearing 5-veined because the 2 veins adjacent to the central ones are incomplete, visible only towards the apex, with a germination flap, falling with the glumes; fertile palea smooth, lustrous, similar to the fertile lemma; stamens 3; anthers ca. 2 mm long; caryopsis oblong, embryo ca. one half as long as the caryopsis, hilum oblong, one fourth as long as the caryopsis.

Additional specimen examined:— MEXICO. Jalisco. Mpio. Talpa de Allende: Minas de Zimapan por la brecha a Cuale, bosque de pino y encino, 1620 m, 12 December 1981, F. J. Santana-Michel 889 ( IBUG, XAL).

Etymology:— The specific epithet refers to the presence of glandular spots throughout the plant (internodes, sheaths, inflorescence and spikelets).

Distribution, habitat, and ecology:— Dichanthelium multiglandulosum is endemic to the area of Talpa de Allende, in the northwestern part of Jalisco ( Fig. 4 ). It occurs on humid slopes in oak-pine forest, at elevations between 1620 and 2100 m.

Phenology:— Flowering in December and January.

Diagnostic characters:— Cane-like habit, plants 120–140 cm tall, glandular spots throughout the plant (internodes, sheaths, inflorescence and spikelets, Fig. 2 ), and glabrous spikelets 3.5–4.3 mm.

Spikelet micromorphology:— The micromorphology of the bracts and fertile floret is simple: the glumes and sterile lemma are glabrous and at the base of both glumes there is a wrinkled area, which may represent a gland. The fertile lemma is smooth and shiny all over, although at high magnification (120×) tiny papillae can be seen ( Fig. 3 ). The apex is acute and umbonate with few tiny antrorse hairs.

Photosynthetic pathway: — Leaf blade cross sections confirm a “non-Kranz” anatomy associated with a C 3 photosynthetic pathway ( Brown & Smith 1975, Zuloaga et al. 1993). As described by Zuloaga et al. (1993) the midrib is a large first order vascular bundle followed by a tandem array of several secondary vascular bundles and a smaller first order vascular bundle up to the margin of the leaf blade. The secondary vascular bundles have an outer bundle sheath with extensions to both surfaces, without specialized chloroplast as shown by Zuloaga et al. (1993). The mesophyll is semiradiate around the vascular bundles, adaxially the cells are in a palisade-like arrangement, and abaxially the cells are in a spongy-like tissue. Vascular bundles are separated by more than five chlorenchymatous mesophyll cells ( Fig. 2 ).

Related species and section affiliation:— The new species was first recognized as “ Panicum multiglandulosum ”

in a revision of Flora Novo-Galiciana ( McVaugh 1983), but was never formally published; the name was also included in a checklist ( Dávila et al. 1998). Based on the anatomy indicating a C 3 photosynthetic pathway, habit, blade shape and spikelet morphology, this species belongs in the genus Dichanthelium . Based on observations and literature ( Zuloaga et al. 1993), this species resembles some other Mexican and South American species lacking a basal rosette and foliar dimorphism. The diagnostic character for which the new species is named is the presence of glandular spots throughout the plant (internodes, sheaths, inflorescence, spikelets). Other species from Mexico and South America have glandular spots on only some organs, not all of them. Other characters, such as the size of the plant and its cane-like habit, further support recognition of the new species. This species, like some Mexican species and most South American species, apparently has only one phase of growth.

Dichanthelium multiglandulosum and a few other species ( D. assurgens ( Renvoize 1982: 325) Zuloaga in Aliscioni et al. (2003: 816), D. commutatum (Schultes in Roemer & Schultes 1824: 242) Gould (1974: 59), D. davidsei ( Zuloaga & Morrone 1991: 158) Zuloaga in Aliscioni et al. (2003: 816), D. itatiaiae ( Swallen (1966: 81) Zuloaga (2003: 816)) distributed from Mexico to South America are the most robust species of the genus that grow like a cane. In Mexico, plants of D. multiglandulosum are the tallest of the genus. Of these, Dichanthelium commutatum (at least the Mexican specimens) is the only species that seems related to D. multiglandulosum , based on the robustness of the plants, lack of winter rosette, sometimes with glandular spots on the sheaths, the lack of indumentum of the synflorescence axis and the wrinkled and possibly glandular base of the spikelets. Following the classifications of Hitchcock & Chase (1910) and Freckmann & Lelong (2003) plus characters such as the habit, the lack of both basal rosette and foliar dimorphism (in the Mexican plants) as well as characters of the spikelets, D. commutatum is placed in section Macrocarpa Freckmann & Lelong (2002: 165)

Placing D. multiglandulosum in section Macrocarpa or any of the other recognized sections of the genus, however, is difficult, because the species does not agree completely with any current sectional circumscription following Freckmann & Lelong (2003). A phylogenetic classification of the genus does not yet exist, but is currently being studied ( Neubig et al. 2015, Majure et al. 2016). The new species may be related to sections including species with membranous-ciliate ligules ( Table 1). Several of these sections, however, such as Nudicaulia Hitchcock & Chase (1910: 142) ex Freckmann & Lelong (2002: 165), Sphaerocarpa (Hitchcock in Robinson & Fernald (1908: 113)) Freckmann & Lelong (2002: 166) and Strigosa Freckmann & Lelong (2002: 165) can be excluded from consideration because their species are smaller plants, form a basal rosette and have much smaller spikelets, even though the species may be glabrous like in D. multiglandulosum . This leaves as the possible groups for the new species sections Pedicellata ( Hitchcock & Chase (1910: 142) ex Freckmann & Lelong (2002: 165)), Clandestina Freckmann & Lelong (2002: 164) and Macrocarpa , which have species that may or may not develop a basal rosette.

The new species is probably not part of section Pedicellata , which includes D. nodatum and D. pedicellatum . These species have slender habits, do not form a basal rosette and have large, obovate to pyriform, papillose-pilose and attenuate-based spikelets, with ligules in one species pilose and in the other membranous-ciliate. The section Clandestina is also ruled out, because in its species the basal rosette is well differentiated, the spikelets are smaller, the rhizomes are thick and the plants are densely branched above. Macrocarpa is the section that shares the most characters with D. multiglandulosum , but differs by having a “usually well differentiated rosette” and pubescent spikelets ( Table 1). The more robust species of the genus in North America are classified in sections Macrocarpa , which includes previously recognized groups such as Commutata Hitchcock in Robinson & Fernald (1908: 113) and Latifolia Hitchcock in Robinson & Fernald (1908: 116), and section Clandestina . I propose to include the new species in section Macrocarpa , with the caveat the circumscription of the section needs to be expanded to include species without a basal rosette and with glabrous spikelets, otherwise the species would remain unclassified as the South American species. Molecular data are needed to test this hypothesis of relationship.

In Mexico, section Macrocarpa was previously represented by two species, Dichanthelium commutatum and D. macrospermum . The latter species is discussed in the next section and is proposed as a synonym of the new name D. transiens . These two species and D. multiglandulosum now make up section Macrocarpa in Mexico. In Table 2 differences and similarities among these three species are summarized.

Figures

FIGURE 1. Dichanthelium multiglandulosum. A. Cane-like habit. B. Ligular area (arrow pointing to the ligule) showing the adaxial surface of the leaf. C. Synflorescence branching pattern. D. Spikelet, first and second glume view.E. Fertile floret, fertile lemma and fertile palea view. (Based on the type)

FIGURE 2. Photographs showing the glandular spots on internodes (A), and synflorescence (axis, branches and pedicels) (B) and leaf blade cross section (C) of Dichanthelium multiglandulosum.

FIGURE 3. Micromorphology of the spikelet and fertile lemma of Dichanthelium multiglandulosum (A. Spikelet second glume view. B. Fertile lemma. C. Fertile lemma apex) and D. transiens (D. Spikelet second glume view. E. Fertile lemma. F. Fertile lemma apex).

FIGURE 4. Distribution of Dichanthelium transiens (¡) and D. multiglandulosum (●).