Dichanthelium arenicollinum, LeBlond & S. C. Carr, 2024

Dichanthelium arenicollinum ( Poaceae ), a new species from peninsular Florida

A new species of Dichanthelium is described from dry pine/oak sandhills in Clay and Volusia counties in northern peninsular Florida. It was discovered by Carr at two locations in northern peninsular Florida and has strong credentials as a new species in sect. Pedicellata . This section previously included two species, D. pedicellatum (Vasey) Gould and D. nodatum (Hitchc. & Chase) Gould , both restricted to Texas and Mexico (and Guatemala for D. nodatum ) ( Freckmann & Lelong 2003). Distinguishing characteristics of the section include hard, cormlike bases, absence of a basal rosette, large basal leaves, and basally attenuate spikelets. The novel species differs from the other members of the section by several characters of the spikelets. Both Florida locations are on ridgetops in pine/oak sandhill habitat, inspiring the Latin epithet for “sandhill, ” arenicollinum .

Dichanthelium arenicollinum LeBlond & S.C. Carr , sp. nov. ( Fig. 21 View FIG ). TYPE: U.S. A. FLORIDA: Clay Co.: Jennings State Forest , ridgetop sandhill with mature open pine/oak canopy, lat. 30.180028N,long.– 81.935917W, 23 Apr 2023, Carr s.n. (HOLOTYPE: NCU; ISOTYPES: FLAS, US) GoogleMaps .

Diagnosis.— Dichanthelium arenicollinum shares the basal features and attenuated spikelets of D. pedicellatum and D. nodatum , but differs from both by having shorter and narrower spikelets, shorter lower glumes, and shorter and relatively wider upper florets.

Description.— Vernal culms 1-few, 30–80 cm long, cespitose to short-rhizomatous, bases hardened, thickened, 3–4 mm wide at emergence from root crown. Internodes 1.3–1.5 mm wide to 20 cm long, proximal internodes moderately densely ascending-appressed (-retrorse) pilose with hairs about 2 mm long, distal internodes becoming less densely and appressed pilose. Nodes densely bearded with spreading to spreading-retrorse hairs 1.5–2.5 mm long, becoming glabrate in age. Basal rosettes absent. Leaf sheaths shorter to much shorter than internodes, the ascending pubescence increasing distally on individual sheaths. Ligule a minute membrane with cilia <1 mm long but vernal blades with a pseudoligule up to 8 mm long behind it. Culm blades 4–5, 5–13 cm long × 4–11 mm wide, averaging 15 × or more as long as wide, margins scabrous and often ciliate for most of their lengths with hairs to 6 mm long; basal blades largest, blades quickly becoming smaller and less ciliate upwardly on culm, the hairs emanating from the blade surface closely adjacent to the margin; blade surfaces densely appressed-pubescent abaxially, becoming less so upward on the culm, adaxial surface glabrous to glabrate, bases narrowly rounded to clasping; uppermost blade (flag) 2.8–5.2 cm long × 3–5 mm wide. Peduncles 10–20 cm long × 0.5–0.7 mm wide, moderately ascending pilose with hairs to 1 mm long, these continuing into the panicle rachis, the branches and pedicels glabrous. Panicles 5–9 cm long × 5–8 cm wide, the branches widely spreading, pedicels 2–23 mm long. Spikelets mostly purplish, 2.3–2.7 mm long × 1.2–1.5 mm wide, elliptic to obovoid, basally attenuate, moderately to densely pubescent with spreading hairs 0.2–0.4 mm long. Lower glumes 0.9–1.3 mm long, ovate-acute to deltoid-triangular, attached about 0.2–0.4 mm below expansion of upper glume and lower lemma, their bases nearly or completely encircling the pedicel. Upper glume and lower lemma equaling upper lemma (or the upper glume sub-equaling). Upper lemma 2.0– 2.1 mm long × 1.2–1.4 mm wide, apex glabrous. Autumnal blades 1.8–6.0 cm long × 1.5–4 mm wide, glabrous adaxially, glabrous to sparsely pilose abaxially. Autumnal spikelets stramineous, 2.6–2.9 mm long × 1.0– 1.1 mm wide before divergence of glumes away from central axis.

Additional collections. FLORIDA. Clay Co.: Jennings State Forest, ridgetop sandhill with mature open pine/oak canopy, lat. 30.180028N, long.– 81.935917W, 6 Nov 2001, Carr s.n. (PARATYPE: MO). Volusia Co. : sandhill south of state route 40, Heart Island Conservation Area ,lat. 29.184117,long.-81.34615, 17 Dec 2002, Carr s.n. (PARATYPE: FSU) GoogleMaps .

Distribution and ecology.— Dichanthelium arenicollinum is currently known only from the two localities on peninsular Florida. Habitat at the Clay Co. site in Jennings State Forest is a ridgetop sandhill with evidence of recent fire and likely with a history of frequent fire. The open mature canopy is dominated by Pinus palustris Mill. , with an oak understory of Quercus laevis Walter , Q. incana W. Bartram , and Q. margaretiae (Ashe) Small. Prominent ground layer plants include Aristida beyrichiana Trin. & Rupr. , Castanea pumila (L.) Mill. and Serenoa repens (W. Bartram) Small. The Volusia Co. site in Heart Island Conservation Area is a ridgetop sandhill where most of the pine canopy has been removed, with exotic pasture grasses present in patches. Quercus laevis , Q. incana and Q. geminata Small form an understory over Aristida beyrichiana , Eremochloa ophiuroides (Munro) Hack. , Sorghastrum secundum (Elliott) Nash , Schizachyrium scoparium (Michx.) Nash var. stoloniferum (Nash) J. Wipff , and Tephrosia chrysophylla Pursh. Dichanthelium malacon also occurs at this site.

Discussion.— Regarding the absence of a basal rosette, in Dichanthelium that is a common occurrence in collected specimens and does not necessarily mean that the plant will not produce one later. Also, some species produce basal rosettes in temperate regions but not in tropical regions. The plants in sect. Pedicellata have never been observed to produce a basal rosette and instead produce basal offshoots with leaves that are among the largest on the plant, though these are frequently not collected, especially in D. nodatum specimens. Silveus (1942) describes basal offshoots in both Texas taxa: “Late in the fall shoots appear at the base of plants with blades 2–4” [5–10 cm] long, 7–10 mm wide, prominently papillose-ciliate with sheaths more densely hirsute than those of the mature culms. These shoots somewhat resemble a winter rosette, but they later develop into flowering culms.” The largest leaf blades in Dichanthelium arenicollinum are 13 cm long × 11 mm wide and are basal.

Autumnal spikelets of Dichanthelium arenicollinum are 2.6–2.9 mm long × 1.0– 1.1 mm wide, while those of vernal spikelets are 2.3–2.7 mm long × 1.2–1.5 mm wide; the autumnal spikelets are also more strongly attenuate basally. The glumes and lower lemma of autumnal spikelets diverge from the central axis by as much as 45 degrees or more, similar to the habit of D.malacon (Nash) LeBlond. It is most readily distinguished from the other members of sect. Pedicellata by the following floral characters: