Biscayne spleenwort

Asplenium rhizophyllum Linnaeus var. biscayneanum D. C. Eaton, Bull. Torrey Bot. Club 14: 97, plate 168. 1887

Roots proliferous. Stems erect, not branched; scales blackish throughout, linear-deltate, sparse, 1--1.3 × 0.1--2.4 mm, margins entire. Leaves nearly monomorphic. Petiole green, becoming blackish in older leaves, 1--5(--12) cm, 1/8--1/3 length of blade; indument of black, narrowly lanceolate scales. Blade dull, linear, 2-pinnate, (4--)12--22 × 1--3.5 cm, papery, glabrous; base slightly tapered; apex narrowing gradually, not rooting. Rachis mostly blackish, green distally and in juvenile leaves, shiny, sparsely scaly. Pinnae in 9--20 pairs, oblong, 0.5--2 × 0.4--1.3 cm; apex blunt to truncate. Pinnules of 1--2 segments; segments linear-oblong, 3--6 × 1--3 mm; margins dentate; apex notched, pointed, rounded, or blunt. Veins free, evident. Sori 1--2 per segment, on both basiscopic and acroscopic sides. Spores abortive. 2 n = ca. 180.

Hammocks, on limestone rock faces; 0--20 m; Fla.

Asplenium × biscayneanum is the hybrid of A . trichomanes-dentatum and A . verecundum , with which it occurs. This peculiar spleenwort may most readily be separated from A . trichomanes-dentatum by its deeply cut pinnae, and from A . verecundum by being only 2-pinnate and having long petioles. Chromosome pairing in A . × biscayneanum is irregular. Judging from herbarium collections, it shows considerable hybrid vigor. All the collections are from Dade County, Florida, where it may now be extirpated.