4. Asplenium rhizophyllum Linnaeus, Sp. Pl. 2: 1078. 1753.
Walking fern, doradille ambulante Camptosorus rhizophyllus
(Linnaeus) Link Roots not proliferous. Stems erect or ascending,
usually unbranched; scales dark brown throughout, narrowly
deltate, 2--3 × (0.2--)0.5--1 mm, margins entire. Leaves
monomorphic but fertile leaves generally larger than sterile
leaves. Petiole reddish brown at base, becoming green distally,
dull but sometimes lustrous at base, 0.5--12 cm, 0.1--1.5 times
length of blade; indument of dark brown, narrowly deltate scales
at base, of minute, club-shaped hairs distally. Blades highly
variable in size and shape, even on 1 plant, narrowly deltate to
linear-lanceolate, simple, 1--30 × 0.5--5 cm, leathery, sparsely
pubescent, hairs more numerous abaxially than adaxially; blade
base cordate, auriculate, or occasionally hastate, auricles
rarely attenuate and radicant; margins entire to sinuate, rarely
irregularly incised; apex rounded to very long-attenuate and, if
attenuate, generally rooti