Pellaea ternifolia

Pellaea ternifolia (Cav.) Link
(Latin: terni, in three’s, and folius, leaved, = with three leaves, in reference to the pinnae which are deeply divided into three portions)

Local names: Trans-Pecos cliff-brake, ternate cliff-brake

Plant to 50 cm tall; rhizome scales with 2 distinct colors, black in center with brown along margins; petioles dark purple to black, shiny; leaf blades with all or almost all pinnae deeply ternately divided (= into three por-tions) (1–5+ pinnae at leaf tip can be entire), the blade thus 2-pinnate-pinnatifid throughout, 2–8.5 cm wide, monomorphic; rachis glabrous or with only a few scattered hairs; pinnae attached to rachis so that their tips point } straight out or slightly towards tip of leaf; ultimate leaf segments linear-oblong, apically mucronate, leathery, completely glabrous on lower surface; 2n = 58 or 116. Cliffs, rocky slopes, ledges, on igneous substrates; Trans-Pecos. Sporulating May–Oct. [Pteris ternifolia Cav.] This species has the “most extensive distribution of any species in the genus” (Windham & Yatskievych 2003a); it ranges from the sw U.S. and Mexico to Chile, with disjunct populations in Hawaii and Hispaniola (Tryon 1957; Windham & Yatskievych 2003a). Yarborough and Powell (2002) consider this species to be rare in TX. Currently, three subspecies are recognized within P. ternifolia (Mickel & Smith 2004); one (subsp. arizonica) occurs in the sw U.S. and Mexico and disjunctly in SC, another (subsp. ternifolia) in TX, Mexico to South America, and Hawaii, and the third, subsp. brandegeei (C.C. Hall) Mickel, in Baja California, Mexico and in Hawaii. Subspecies brandegeei differs from the other two in having the pinnae short-stalked (the stalks [technically petiolules] 1–2 mm long) versus sessile. Windham (1993c) noted that the two subspecies occurring in TX are separated by chromosome number and minor morphological differences, and that they “show a tendency toward geographic isolation.” At one time Windham (1993c) treated P. villosa as a subsp. of P. ternifolia (see discussion under P. villosa). Windham (1993c) separated subsp. arizonica and subsp. ternifolia as follows:

1. Largest ultimate segments (excluding terminal pinnae) usually more than 18 mm; distal portion of petioles rounded or slightly flattened adaxially; spores usually 46–53 μm diam._______subsp. arizonica
1. Largest ultimate segments (excluding terminal pinnae) usually less than 18 mm; distal portion of petioles grooved or flattened adaxially; spores usually 39–45 μm diam._______ subsp. ternifolia

subsp. arizonica Windham
(of Arizona, where the type specimen was collected)

Local names: Arizona cliff-brake

Plants similar to subsp. ternifolia, glabrous or essentially so, the rachis glabrous or with a few widely scattered hairs (in contrast to P. villosa); 2n = 116 (Windham 1993c). In TX known only from Brewster Co. (O.E. Sperry s.n. 1936, Chisos Mts., SRSC, annotated by M.D. Windham and mapped by Windham 1993c); in the U.S. known only from AZ and TX in the sw and also remarkably disjunct to the southern Appalachians in SC (Heafner 2001); also Mexico. The SC population was originally identified as P. wrightiana (Platt & Townsend 1996); however, Heafner (2001) has shown that it is actually P. ternifolia subsp. arizonica. It is one of a number of ferns found primarily in the sw or w U.S. with isolated disjunct populations in the southern Appalachians (see discussion on page 31). This subspecies is represented by tetraploids (Windham 1993c). A hybrid between P. ternifolia subsp. arizonica and P. wrightiana is known from the Chisos Mts., Brewster Co. (Soxman 246-X, TEX-LL, identified by M.D. Windham). Because of its rareness and limited distribution in the state, we consider this subspecies to be of conservation concern in TX.

subsp. ternifolia

Local names: trans-pecos cliff-brake

Plants glabrous or essentially so, the rachis glabrous or with a few widely scattered hairs; largest ultimate segments (excluding terminal pinnae) usually less than 18 mm, but occasionally slightly more (e.g., 21 mm on a BRIT sheet [Correll 13684A] annotated by M.D. Windham); 2n = 58 (Windham 1993c). Known in the U.S. only from the Chisos Mts., Brewster Co. (M.S. Young s.n., 1915, BRIT—annotated M. Windham; Correll 13684A, BRIT, TEX-LL—both annotated M. Windham; Windham 1993c) and the Capote Falls area, Presidio Co. (Johnston et al. 10668, TEX-LL); also Mexico to South America and Hispanola and Hawaii. This subspecies is represented by diploids (Windham 1993c). Either of the two subspecies of P. ternifolia occurring in TX could be confused with P. villosa. However, that species has many pinnae entire (not ternately divided) and rachises that are villous (= with long, soft, spreading hairs). Because of its rareness and limited distribution in the state, we consider this subspecies and the species as a whole to be of conservation concern in TX.

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