Adiantum fragile Sw.

  • Authority

    Proctor, George R. 1989. Ferns of Puerto Rico and the Virgin Islands. Mem. New York Bot. Gard. 53: 1-389.

  • Family

    Pteridaceae

  • Scientific Name

    Adiantum fragile Sw.

  • Description

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    Species Description - Rhizome short, thick, often several-branched, densely clothed with bright yellowish-brown, subclathrate, deltate-attenuate to lance-linear scales 1-3.5 mm long, these with denticulateciliolate margins, and those ofthe extreme apex with contorted-filiform tips. Fronds closely clustered, ascending or spreading, 15-60 cm long; stipes lustrous purple-brown, much shorter than the blades, terete, wiry, and glabrous. Blades lance-ovate, 10-45 cm long, 4-18 cm broad, 3- to 4-pinnate at base; pinnae altemate, stalked, with distant oblique pinnules; ultimate pinnules obovate-cuneate, 4-20 mm long, 3-13 mm broad, on stalks 1-3 mm long, very easily breaking off; sterile pinnules denticulate, the ultimate veinlets ending in the teeth; tissue delicately to firmly herbaceous. Sori subreniform to oblong, bome singly or in pairs on very shallow lobes of the rounded distal margin; indusioid flap pale brown, delicately translucent toward margin.

  • Discussion

    Type. Swartz, from Jamaica (S; isotypes SBT; Herb. Willd. 20098, B).

    Syn. Adiantum parvifolium Fee, Mem. foug. 7: 27, t. 23, fig. 2. 1857, (Type. Poiteau, from Hispaniola, RB.)

    Two moderately distinct variants of this species occur in Puerto Rico, both of them quite common. They can be distinguished as follows:

    a. Ultimate pinnules mostly 10-20 mm long; tissue light green, thin-membranous, glabrous, and nonglandular on both sides 14a. war. fragile.

    a. Ultimate pinnules mostly 4-10 mm long; tissue green or slightly glaucous, firm-membranous, usually very minutely puberulous on abaxial side and with numerous minute resinous glands embedded in the abaxial epidermis

    14b. var. rigidulum.