A new peltate-leaved taxon of Psacalium, Psacalium putlanum, is described and illustrated from southwestern Oaxaca, Mexico. It appears to be closely related to the widespread P. peltigerum. Additionally, the closely related P. peltigerum var. latilobum Pippen of Guerrero is elevated to specific rank as P. latilobum (Pippen) B.L. Turner. A phototype and drawing of P. putlanum are provided, along with a map showing the distribution of the taxa concerned.
The following names and/or taxa are proposed, both related to Pasacalium peltigerum, as noted in the account that follows:
Type: MEXICO. OAXACA: Distrito Putla, Mpio. Santa Cruz Itundujia, Camino al Agua del Plantanal a 2.31 km en LR (S) de la Agencia de Iturbide. Selva baja caducifolia, 16° 41′ 47.45″ N, 97° 34′ 17.8″ W, ca. 1110 m, Kenia V. Gutierrez 2792 [con M. Trujillo y H. Cruz] (Holotype: TEX).
Psacalium peltigerum (B. L. Rob. & Seat.) Rydb. similes sed caulibus dense gossypino-pubescentibus, foliis crassioribus, capitulis minoribus (bracteis involucralibus 5–6 mm longis vs. 7–8 mm), faucibus corollarum 1–2 mm longis (vs. caventibus) et acheniis 5- nervatis (vs. 9-nervatis).
Robust herbs 0.6–1.2 m high, arising from thick ligneous roots. Stems stiffly erect, perennial, 0.6–1.0 cm thick at mid-stem, bearing 2–3, distantly spaced leaves, densely cottony pubescent, especially below. LEAVES alternate, peltate, the petioles 6–30 cm long, pubescent like the stems; blades thickened and deeply incised, the divisions 4–12 cm long, 2–5 cm wide, pinnately veined, their margins irregularly serrate. Capitulescence a terminal, corymbose panicle, 50–60 cm high, the ultimate peduncles 1–3 cm long. Involucres narrowly campanulate, ca 3 mm wide, the bracts 5, 5–6 mm long, glabrous, ebracteate or nearly so. Florets 4–5, ray florets absent. Corollas creamy white, glabrous, ca. 8 mm long; tubes 1–2 mm long; throats 1–2 mm long; lobes 3–4 mm long. Anthers pale brown, ca. 3 mm long, appendages lanceolate. Achenes black, glabrous, 5-ribbed; pappus of numerous, tawny-white, persistent bristles, 5–6 mm long.
The novelty is clearly related to Psacalium peltigerum and P. hintonii (Pippen) H. Rob. & Brettell, of more northerly climes (Fig. 3), and will key directly to the former taxon in the accounts of both Pippen (1968) and Robinson and Brettell (1973). It is readily distinguished from P. peltigerum by a number of characters, as noted in the above diagnosis. The following key well help in their identification:
1. Stems glabrous, or glabrate P. peltigerum
1. Stems sparsely to densely puberulent (2)
2. Leaves with broad linear lobes; stems densely cottony-pubescent P. putlanum
2. Leaves with deltoid lobes; stems sparsely puberulent P. latilobum
The species is named for the Distrito Putla, whence the type
Additional specimen examined: MEXICO. OAXACA: A 300 m en LR (N) de la colonia Agua del Platanal, Agencia de Iturbide, ca 968 m, 18 Jun 2008, Gutierrez 2743 (TEX).
Psacalium latilobum (Pippen) B.L. Turner,
Based upon Psacalium peltigerum var. latilobum Pippen, Contr. U.S. Natl. Herb. 34: 431. 1968.
The type of this taxon is from southcentral Guerrero (Fig. 3) and appears to be as distinct as Pasacalium hintonii, which Robinson and Brettell (1973) elevated to specific rank from its varietal position within P. peltigerum.
Thanks to my colleague Guy Nesom for the Latin diagnosis and proofing the manuscript. Mr. T. P. Weeraratne provided the line drawings.