Chusquea section Tenellae L. G. Clark, 2017

Attigala, Lakshmi, Fuentes, Alfredo F. & Clark, Lynn G., 2017, Chusquea sect. Tenellae (Bambuseae, Bambusoideae, Poaceae), a taxonomic revision of a new section from South America, Phytotaxa 324 (3), pp. 239-265 : 244-246

Chusquea section Tenellae L. G. Clark , sect. nov. — TYPE: Chusquea tenella Nees

Diagnosis: — Differs from all other sections recognized within Chusquea subg. Chusquea by the presence of pseudopetiolate culm leaf blades that remain green; a bud complement with a set of 1–4 strongly laterally compressed, + falcate subsidiary buds on each side positioned facing each other, with the top-most bud of each set larger than the others; synflorescences borne on a mix of longer leafy and shorter non-leafy subsidiary branches per node; and thin-textured spikelets with glumes I and II small and scale-like.

Description: — Plants growing in diffuse colonies. Culms 3–5 (–8) m tall/long, (0.3–) 0.5–1 (–1.5) cm in diameter, erect at the base, arching and becoming trailing or scandent, clambering or hanging above; internodes 15–32 (–36) cm long, terete, usually solid or sometimes irregularly hollow. Culm leaves with sheaths persistent, usually striate near the base, a sheath summit extension almost always present on at least one side, often on both, but the one extending from the underlapping margin longer; girdle 0.5–5 mm wide; outer ligule present; inner ligule variable in size but asymmetrical, adnate to the longer sheath summit extension; blades pseudopetiolate, spreading to reflexed (erect in one species), remaining green but eventually deciduous. Nodes at mid-culm with one central bud, this parallel-sided but with a broadly triangular apex, subtended by a cluster of 5‒37 smaller subsidiary buds of two sizes, with a set of 1–4 strongly laterally compressed, + falcate subsidiary buds on each side facing each other, the top-most bud larger than the others, and the remaining subsidiary buds smaller and positioned in between the two lateral sets, often in a triangular arrangement; the nodal line dipping slightly to markedly below the bud/branch complement; the supranodal ridge more or less conspicuous but the same diameter as the nodal line. Branching infravaginal; central branch often developing at the same time as the subsidiaries or later, subsidiary branches of two sizes (rarely subequal), both usually rebranching. Foliage leaves with the sheaths often maculate when young, keeled, a sheath summit extension almost always present on at least one side, often on both, but the one extending from the underlapping margin longer; pseudopetioles usually pulvinate; blades lanceolate to ovate, base usually asymmetrical, midrib excentric (sometimes + centric). Synflorescences 1.5–10 cm long, 0.5–2 cm wide, racemose or paniculate, with branches and pedicels appressed to the rachis or spreading and diffuse, borne on a mix of longer leafy and shorter non-leafy subsidiary branches per node; rachis and pedicels angular, pedicels 0.4–14 mm long. Spikelets (7.5–) 8.5–11.5 (–12.4) mm long, 1.5–2.8 mm wide, + laterally compressed, thin-textured (membranaceous); glumes I and II scale-like, no more than 1/10 the spikelet length, usually glabrous, nerves usually absent (sometimes glume II weakly 1–2-nerved); glumes III and IV 1/3–2/3 the spikelet length, triangular to navicular; lemma and palea subequal, the lemma navicular, the palea 4–6-nerved. Lodicules 3, membranaceous, ciliate. Stamens 3; anthers yellow. Gynoecium with styles 2, stigmas 2, weakly to strongly plumose. Fruit not seen.

Comments— As presented in the diagnosis above, Chusquea sect. Tenellae is easily distinguished from the other sections of Chusquea subg. Chusquea by its unique culm leaf structure, bud morphology and organization, dimorphic leaf development on flowering branches and spikelet texture ( Table 2). The other five sections all share triangular, non-pseudopetiolate and erect culm leaf blades the same color as the sheath; triangular or circular central buds; synflorescences borne on subequal leafy subsidiary branches; and chartaceous spikelets. However, three of these five sections [sect. Longiprophyllae Clark (1990: 626) , sect. Serpentes Clark (1989: 91) and sect. Verticillatae Clark (1989: 74)] also exhibit their own unique characters or unique combinations of vegetative or reproductive characters ( Table 2). Although the combination of 18–80 subsidiary buds per node, infravaginal branching, and typically linear foliage leaf blades is usually sufficient to diagnose sect. Longifoliae Clark (1989: 105) , each of these features is characteristic of at least one other section in subgenus Chusquea . Sect. Chusquea is characterized by a similar number (15–80) of subsidiary buds per node as sect. Longifoliae , but has extravaginal branching and its foliage leaf blade shape varies from linear to lanceolate.

erect; = sheath in erect; = sheath in = sheath in color erect; = sheath in pseudopetiolate, = sheath in color color color color usually spreading to reflexed; green for an extended period Branching extravaginal infravaginal infravaginal infravaginal 1 infravaginal modified 2 pattern extravaginal,

less commonly infravaginal or modified infravaginal Central bud triangular (less triangular (less triangular triangular (less parallel-sided with triangular or circular outline commonly commonly commonly a broadly triangular circular) circular) circular) apex Central bud truncated at bud truncated at bud elongated (3‒10 cm truncated at bud truncated at bud apex truncated at bud apex prophyll apex apex long) apex Subsidiary 15‒80 per node, 18‒80 per node, 10‒40 per node, 2‒12 per node, 5‒37 per node, of (8‒) 30‒100 per node, bud number, subequal, in 1‒3 subequal, in (1‒) subequal, in a tight subequal, in 1 two sizes, a set of subequal (rarely size and constellate rows 2‒4 constellate circular cluster constellate row 1–4 strongly laterally of two sizes), in arrangement rows subtending the central compressed, + falcate (1‒) 2‒3 rows either bud/branch buds on each side nearly encircling the facing each other, central bud/branch or the top-most larger completely (or nearly than the others, completely) encircling the remaining the node buds smaller and positioned in between the two lateral sets Foliage leaf linear to linear (to linear- lanceolate (to linear- or ovate or ovate- lanceolate to ovate lanceolate to ovateblade shape lanceolate lanceolate) ovate-lanceolate) lanceolate lanceolate Synflorescence subequal leafy subequal leafy subequal leafy branches subequal leafy longer leafy and subequal leafy branch length branches branches branches shorter non-leafy branches and leaf branches development Spikelet lateral lateral lateral lateral lateral dorsal compression Spikelet texture chartaceous chartaceous chartaceous chartaceous membranaceous chartaceous Development reduced or developed,> 1/10 developed,> 1/10 developed,> 1/10 reduced, <1/10 reduced, <1/10 of glumes I developed and spikelet length, spikelet length, glume spikelet length, spikelet length, often spikelet length, often and II> 1/10 spikelet glume II longer II 2× glume I glume II> glume scale-like, subequal scale-like, subequal length, subequal than but not up to I, sometimes up or glume II longer 2× glume I to 2×

than but not up to

2× glume I 1 Two Mexican species [ C. enigmatica Ruiz-Sanchez, Mejía-Saulés & Clark ( Ruiz-Sanchez et al. 2014: 20) and C. gibcooperi Ruiz-Sanchez, Mejía-Saulés, Cortés & Clark ( Ruiz-Sanchez et al. 2015: 228) ] previously classified in this section have both intravaginal and extravaginal branching on the same culm; they are misclassified in this section and are here considered to be Incertae Sedis within Chusquea subg. Chusquea . 2 Here, whether describing extravaginal or infravaginal branching, “modified” indicates that culm leaf is deciduous early in the development of the branch complement.

Rhizome morphology is unevenly documented across the diversity of Chusquea and for this reason is not included in Table 2, although it may eventually prove informative in distinguishing among some groups ( Clark 1989, Mota 2013). Chusquea subg. Magnifoliae , subg. Platonia , subg. Swallenochloa and sects. Longifoliae , Longiprophyllae (inferred from the clumping habit) and Verticillatae of subg. Chusquea are characterized by pachymorph rhizomes ( Clark 1989, 1990; Clark, pers. obs.), but rhizome morphology is poorly documented for subg. Rettbergia ( Mota 2013, Mota et al. 2017). As noted above, the amphimorph condition is inferred for sect. Tenellae , but direct observations are needed. The scandent, sprawling or trailing habit of most members of sect. Serpentes ( Clark 1989) also suggests the possibility of amphimorph rhizomes, but again, this remains to be confirmed by direct observation. However, amphimorph rhizomes are confirmed for a number of species in sect. Chusquea , although it remains to be determined whether this is a consistent feature of the section ( Clark 1986; Clark, pers. obs.).

The Chusquea meyeriana informal group, as noted in the Introduction, is characterized by reflexed lower inflorescence branches and the usual presence of one or more spatheate bracts subtending the inflorescence ( Fisher et al. 2014). This Brazilian group requires additional study before its status within subg. Chusquea can be determined, and thus is not included in Table 2.