Rhipidocladum singuliflorum Ruiz-Sanchez & C.D.Tyrrell, 2022

Ruiz-Sanchez, Eduardo, Tyrrell, Christopher D., Carrillo-Reyes, Pablo & Nuno-Rubio, A. T., 2022, A striking new species of Rhipidocladum (Poaceae: Bambusoideae: Bambuseae: Arthrostylidiinae) with single, terminal-spikelet synflorescences, endemic to Jalisco, Mexico, Plant Ecology and Evolution 155 (3), pp. 417-424 : 417

Rhipidocladum singuliflorum Ruiz-Sanchez & C.D.Tyrrell sp. nov.

Figs 2 , 3 , 4

Type.

MEXICO - Jalisco • Puerto Vallarta, Rio Palo Maria ; 20°33 ’8.76” N, 105°15 ’34” W; 6 m; 10 Dec. 2021; fl.; E. Ruiz-Sanchez, A.T. Nuño, A. Zabalgoitia, L.A. Monroy & L. Campos 722; holotype: IBUG; isotypes: MEXU, ZEA .

Diagnosis.

Rhipidocladum singuliflorum differs from R. barbinode and R. racemiflorum by having a single terminal spikelet. Meanwhile, R. barbinode has a spicate synflorescence with 3-7 spikelets and R. racemiflorum has a raceme synflorescence with 10-13 spikelets. R. singuliflorum has efimbriate or poorly developed fimbriae on the foliage leaves, meanwhile, R. barbinode and R. racemiflorum bear fimbriae at the apex of the sheath of the foliage leaves.

Description.

Culm height 3-10 m. Internodes smooth, uniform in colour, 9-33 cm long, 3-9 mm in diameter, hollow (pithy when young); walls 2-3 mm thick. Culm leaves 17-19 cm long; sheaths (6.5-)7.6-9(-9.9) cm long, abaxially glabrous, adaxially glabrous and shiny; blades erect, 9-10 cm long, abaxially sparsely pubescent at the base, adaxially glabrous, margins entire; fimbriae not seen. Branch complements at mid-culm nodes with (30-)41-87(-120) branchlets; branchlets (8-)13-30(-50) cm long, glabrous or pubescent. Foliage leaves 3-4 observed on flowering branchlets; sheaths 9-22 mm long, abaxially pubescent (occasionally glabrous); mostly efimbriate, when fimbriate 0.2-0.8 mm long, white to stramineous; pseudopetioles 1.0-1.6 mm long, abaxially and adaxially pubescent; blades lanceolate to narrowly ovate with an attenuate apex, 32-75 mm long, 5-7 mm wide, abaxially and adaxially glabrous, without sparse patches of white cilia near the base on the abaxial side. Synflorescences 2.0-3.4 cm long, 0.9-10 mm wide, composed of a single spike, sometimes develop two spikelets, one of them with only two florets; rachis pubescent. Spikelets 2.0-3.4 cm long, comprising 2-4 glumes and (2-)4-5(-20) fertile florets, rachilla joints 3.5-4 mm long, glabrous. Glumes pubescent margins ciliate, awnless, lower glume, 3.2-5.8 mm long, 6-, 9-, 10-nerved, lanceolate; upper glume, 4.8-7.0 mm long, 11-, 13-nerved, lanceolate. Lemmas 8.8-12.0 mm long, 9-, 13-nerved, ovate and inflated, pubescent, apex rounded-obtuse and muticous. Palea 10.0-13.6 mm long, keels and sulcus pubescent, apex rounded-obtuse and muticous. Lodicules 3, abaxially glabrous, hyaline, margin ciliate apex fimbriate, the anterior pair 2.6-3.2 mm long, the posterior one 2.0-2.4 mm long. Anthers 3. Ovary 1.0-1.5 mm long, stigmas 2, plumose. Caryopsis 3.3-3.5 mm long, ellipsoid, pubescent with trichomes near base and apex, indented on hilum side, yellowish-golden.

Distribution.

This species is only known from three localities in the municipality of Puerto Vallarta, Jalisco, Mexico in the Jalisciense-Tuito district of the Sierra Madre del Sur ( Santiago-Alvarado et al. 2016) (Fig. 1 ).

Habitat and ecology.

This species inhabits the slopes of humid canyons of creeks and rivers at 6-150 m a.s.l. The vegetation corresponds to subdeciduous and tropical dry forests with associated species, such as Astronium graveolens Jacq., Bursera spp., Casearia arguta Kunth, Cecropia obtusifolia Bertol., Cnidoscolus tepiquensis (Cost. & Gall.) Lundell, Croton schiedeanus Schltdl., Cupania dentata Moc. & Sesse, Dendropanax arboreus (L.) Decne. & Planch., Euphorbia spp., Ficus spp., Guettarda elliptica Sw., Inga laurina (Sw.) Willd., Lonchocarpus spp., Luehea candida Mart., Lysiloma divaricatum (Jacq.) Benth., Ouratea madrensis L.Riley, Pseudobombax ellipticum (Kunth) Dugand, and Zygia conzattii (Standl.) Britton & Rose, among others (Fig. 3A ).

Etymology.

Latin singulus, solitary, and florum, flowered, alluding to usual occurrence of single, terminal spikelet in synflorescence (Figs 2A , 3D-F ). The use of - florum instead of - spiculum is preferred here [cf. R. racemiflorum ].

Preliminary IUCN conservation assessment.

Critically endangered: CR B1ab(iii). Rhipidocladum singuliflorum is known from three localities that are separated by no more than 14 km. Using GeoCAT, the Extent of Occurrence (EOO) was calculated to be 10.6 km2, and the Area of Occupancy to be 12 km2, based on 2 × 2 km cells. The three localities are canyons that are not suitable for agriculture or grazing, and are often used for recreation with one of them (El Nogalito) currently under management by an ecotourism centre. The localities, however, are adjacent to the Carretera Pacífico (Carretera Federal 200), the major west coast highway, and potentially in the path of the planned series of “vía corta" highway expansions. A preliminary category of Critically endangered: CR B1ab(iii) is proposed following the IUCN ( IUCN Standards and Petitions Committee 2022) criteria.

Additional specimens examined.

MEXICO - Jalisco • Puerto Vallarta, 4 km al SE de Playa Grande, subiendo por el Río Pitillal (2.4 km en línea recta); 20°38 ’14” N, 105°10 ’14” W; 120 m; 18 Feb. 2022; fl.; P. Carrillo-Reyes & S. Quijas-Fonseca 10093; IBUG • Arroyo El Nogalito, 0.8 km en línea recta al SE del Ecoparque El Nogalito; 20°33 ’24” N, 105°14 ’10” W; 130 m; 20 Mar. 2022; P. Carrillo-Reyes & A.T. Nuño-Rubio 10106; IBUG • Rio Palo Maria ; 20°33 ’8.76” N, 105°15 ’34” W; 6 m; 16 Nov. 2021; fl.; A.T. Nuño & L. Campos s.n.; IBUG .

Figures

Figure 1. A. Geographical distribution of the species of Rhipidocladum in Mexico based on georeferenced localities of herbarium specimens (Ruiz-Sanchez et al. 2019, 2020, 2021 b). B. Close up to the geographical distribution of R. singuliflorum (red stars) and R. racemiflorum (black circles) in western Jalisco.

Figure 2. Rhipidocladum singuliflorum. A. Culm segment showing foliage leaves complement and synflorescences. B. Culm segment, showing culm leaf sheath and blade. C. Culm leaf sheath and blade abaxial view. D. Spikelet bearing 2 glumes and 5 florets. E. Glumes. F. Floret, lateral (right) and dorsal (left) views. G. Palea, frontal (right) and lateral (left) views. Drawing by Juvenal Aargon Parada based on E. Ruiz-Sanchez, A. Nuno, A. Zabalgoitia L. A. Monroy y L. Campos 722 (IBUG).

Figure 3. Rhipidocladum singuliflorum. A. Panoramic view of the subdeciduous tropical forest glen habitat at the Palo Maria river, culms showing scandent habit. B. Basal clump showing culms habit and culm leaves. C. Cross section and size cut of culm, showing hollow culm with thick wall. D. Synflorescence branches bearing one terminal spikelet. E. Close up of the spikelet showing glumes, lemma, palea and florets. F. Spikelet. Photos by Eduardo Ruiz-Sanchez (A, B, C, E) and Pablo Carrillo-Reyes (D, F).

Figure 4. Rhipidocladum singuliflorum. A. Caryopsis dorsal view. B. Caryopsis ventral view showing indent near the hilum.