Trichanthecium marunguensis Zuloaga

Zuloaga, Fernando Omar, Aliscioni, Sandra, Delfini, Carolina & Salariato, Diego Leonel, 2024, Old World species of Trichanthecium (Poaceae: Panicoideae: Paniceae) including a new species from the Democratic Republic of Congo, Phytotaxa 646 (3), pp. 230-264 : 249-251

9. Trichanthecium marunguensis Zuloaga , sp. nov.

TYPE:— Democratic Republic of Congo. Plateau des Marungu, Mount Kibobwa , 15 February 1970, S. Lisowski, F. Malaisse & J. J. Symoens 9669 (holotype BR [ 0000001222405 !], isotype POZG) . Fig. 9

Plants presumably perennial, base not observed, 60–70 cm tall; culms simple, erect; internodes cylindrical, up to 20 cm long, hollow, glabrous to sparsely hairy with appressed tuberculate hairs; nodes compressed, glabrous. Sheaths striate, open, longer than the internodes, 17–25 cm long, covered with appressed or spreading tuberculate hairs, the margins ciliate. Ligule membranous, laciniate at the apex, 0.6–0.8 mm long, brownish, with long hairs beneath at the base of the blade. Blades lanceolate, 12–20 × 0.4–0.6 cm, flat or with involute borders, rounded at base, the apex acuminate, densely covered, on both surfaces, with long tuberculate hairs, the margins ciliate, midrib manifest. Inflorescence a terminal, contracted panicle, 20 cm long; main axis wavy, glabrous, pulvini glabrous; spikelets appressed and solitary on alternate first-order primary branches, axis of the branches glabrous, pedicels flexuous, claviform, glabrous, 1–3 mm long. Spikelets broadly ellipsoid, 2.2 × 1.2 mm, greenish and tinged with purple; lower glume as long as the spikelet, 5-nerved, glabrous, membranous, with two whitish tuberculate hairs 2–3 mm long toward the apical portion; upper glume as long as the spikelet, 5-nerved, glabrous, membranous, slightly gibbose; lower lemma glumiform, 5-nerved, 2 mm long, glabrous; lower palea elliptic, hyaline, 2 × 1 mm, glabrous; lower flower staminate, anthers 3, 1.8 mm long. Upper anthecium plano-convex, 1.6–1.8 × 1 mm, shorter than the upper glume and lower lemma, whitish, indurate, shiny, with bicellular microhairs at the lemma and palea surface, upper lemma 5-nerved. Caryopsis not seen.

Distribution and habitat: —Endemic to the Marungu high plateau, in grassland at 2000 m elevation. In flower in February.

Notes: — Trichanthecium marunguensis differs from other species of Trichanthecium by its broadly ellipsoid spikelets, the lower glume with two tuberculate hairs, 2–3 mm long, at the apical portion.

Only known from the type collection, this species occurs only in the Marungu high plateau, southwest of Lake Tanganyka in D.R. Congo ( Dessein et al. 2006), which is largely covered by savannas ( Lisowski et al. 1971), dominated by many species of Cyperaceae and Poaceae . The plateau is isolated from other highland areas, therefore forming a sky island of very peculiar environmental and edaphic conditions ( Dessein et al. 2006).

The transverse section of the leaf of Trichanthecium marunguensis showed a flat outline, ribs and furrows scarcely distinguishing, median keel undifferentiated, chlorenchyma cells elongated radially around the vascular bundles, 4–5 mesophyll cells between contiguous vascular bundles, vascular bundles with two sheaths, the outer with parenchymatous globose cells, translucent without specialized chloroplasts and with adaxial and abaxial extensions, 1(–2) seriate, linking the bundle with both epidermis, the inner sheath with mestomatic cells with the walls thickened and also without chloroplasts, the adaxial bulliform cells are inflated in well-defined fan-shaped groups, of 3–6 cells between consecutive vascular bundles, occupying approximately 1/4 of the leaf thickness ( Fig. 2A–C ). The abaxial epidermis of the leaf in surface view with costal and intercostal zones differentiated, costal zones with silica bodies in dumb-bell and nodular shaped, intercostal zones with rectangular cells with undulations in the walls, alternating with intercostal zones with shorter cells, more cuboidal and without marked undulations, stomata with dome-shaped subsidiary cells, separated by a single interstomatal long cell, unicellular macrohairs with some raised epidermal cells surrounding the sunken base, bicellular microhairs and hooks scattered; the adaxial epidermis is similar to the abaxial one, but with square to short rectangular bulliform cells in intercostal zones, and less stomata and macrohairs ( Fig. 2D–E ).

Although the general pattern of leaf anatomy of Trichanthecium marunguensis (Lisowski et al. 9669) agrees with that of a C 3 species, some characters are somewhat distinctive such as the vascular bundles that are closer together than in other C 3 species, with only 4 to 5 mesophyll cells between adjacent bundles, and the presence of adaxial and abaxial parenchymatous extensions of the vascular bundles ( Fig. 2A–C ). These both particular attributes were also reported in the foliar anatomy of Trichanthecium cyanescens and T. wettsteinii ( Zuloaga et al. 2011) . Ellis (1988) analyzed South African species of Panicum s.l. and grouped species C 3 with this type of anatomy in the Group 1b. On the other hand, the C 3 species that lack these attributes were included in the group Group 1a as P. aequinerve . Ellis (1988) mentioned that species of both groups are anatomically related and possibly the distance between adjacent bundles and the parenchymatous extensions of the bundles could depend on the sunlight situation of the specimen. Based on these observations, Ellis (1988) pointed out that both groups are only anatomically recognized but are undoubtedly closely related, an idea that is supported here by the phylogenetic analysis presented.

The analysis of the spikelet of Trichanthecium marunguensis with SEM revealed that the abaxial epidermis of the lower glume has, in the nerved zones, rows of dumb-bell silica bodies, with stomata between nerves; also, elongated bicellular microhairs are distributed mainly in the upper half of the glume; two prominent macrohairs were observed at the apex of the lower glume, each one having an hemispherical cell surrounding the base of the hair ( Fig. 3A–B, D ). The upper anthecium is typically plano-convex with small simple papillae on the upper lemma, scarce in its lower half. Also, elongated bicellular microhairs were observed, with the proximal cells with thicker wall than the distal one, the latter collapsed or sometimes deciduous. The surface of the palea presents similar characteristics to the ones described for the upper lemma, with the addition that some developed prickles were observed in the apex, partially covered by the lemma ( Fig. 3C, E–G ).

Figures

FIGURE 2. Bright-field microscope micrographs of the leaf anatomy of Trichanthecium marunguensis. A–C. Transverse sections. A. Double headed arrows indicate nearby vascularbundles separated by 4–5 mesophyll cells. B. Adaxial groups of bulliform cells fan-shaped are indicated (bg). C. Colorless parenchymatous adaxial and abaxial extensions linking bundles with epidermis (ex) and raised epidermal cells surrounding the base of macrohairs (bm) are indicated. D–E. Adaxial epidermis in superficial view. D. Stomata with dome-shaped subsidiary cells (sc), basal cell of a bicellular microhair (*), and silica body in dumb-bell (sb) are indicated. E. Rows of stomata (st) and the base of a macrohair (mh) areindicated. Scale bars:A, 255 µm, B–C, 95 µm, D, 40 µm, E, 25 µm.

FIGURE 3. Scanning electron micrographs of Trichanthecium marunguensis. A. Dorsal view ofthe apex of the lower glume with two prominent macrohairs. B. Detail of the base of a macrohair, showing the hemispherical cell surrounding its base. C. Upper anthecium in dorsal view. D. Lower glume in dorsal view showing the two macrohairs that are longer than the glume. E. Apex of the lemma with simple papillae and elongated bicellular microhairs (wall of the proximal cell thicker than the distal cell collapsed or deciduous). F. Apex of the upper palea showing simple papillae, bicellular microhairs and prickles in the distal portion. G. Upper anthecium, ventral view. Scale bars: A, C, E–G, 200 µm, B, 100 µm, D, 500 µm.

FIGURE 9. Trichanthecium marunguensis. A. Habit. B. Ligular region. C. Detail of a branch of the inflorescence. D. Spikelet, lateral view. E. Lower glume. F. Upper glume. G. Lower lemma. H. Lower palea, ventral view. I. Lower palea, dorsal view with stamens and lodicules. J. Upper anthecium, dorsal view. K. Upper anthecium, lateral view. L. Upper palea with lodicules and stamens. (Lisowski et al. 9669 BR).