Thelypteris inabonensis

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Thelypteris inabonensis

No Common Name

ListedJuly 2, 1993
FamilyThelypteridaceae (Marsh fern)
DescriptionA ground fern.
HabitatMontane tropical rainforest.
ThreatsHabitat loss by forestry or hurricanes, and collecting for horticultural use.
RangePuerto Rico


Thelypteris inabonensis is a terrestrial fern with an erect, slender rhizome, about 0.2 in (0.5 cm) in diameter, covered at its apex with numerous dark, lustrous-brown, densely hairy scales. The fronds are erect, arching, and up to 24 in (60 cm) long. The blade is narrowly elliptic, and up to 21 in (55 cm) long. The blade consists of 25-30 pairs of pinnae (lobes of the frond), rounded at their apex, and with up to seven pairs of simple veins. The leaf tissue has many short, erect, acicular (needle-like) hairs and lacks glands. The sori (spore-bearing structures) are small, with a densely long-ciliate indusium (a covering tissue), and are located dorsally on the veins. The stipes (or stalks of the fronds) are 2-4 in (5-10 cm) long, covered with grayish, acicular hairs, and with numerous spreading scales similar to those of the rhizome. This species differs from all other Puerto Rican thelypterid ferns in having scales and acicular hairs on the rachis.


T. inabonensis occurs in montane tropical rainforest, where it grows in deeply shaded conditions in a humus-rich forest floor. It grows in moist, mossy forest dominated by sierra palm (Prestoea montana ). It occurs at elevations of 3,670-4,100 ft (1,120-1,250m), near the summit of Cerro Rosa.


T. inabonensis is a locally evolved (or endemic) species that is only known from two sites in Puerto Rico: in Toro Negro Commonwealth Forest in the municipality of Ponce, and near the summit of Cerro Rosa in the municipality of Ciales.


The total known population of the rare fern consists of only about 46 plants. The habitat in Toro Negro Commonwealth Forest supports 34 plants, and that in Cerro Rosa 12 plants. T. inabonensis is a beautiful fern, and is potentially threatened by collecting for sale in the horticultural trade in rare plants. The plant is also potentially threatened by forest management activities. Because of its tiny population and restricted range, the fern is also extremely vulnerable to the devastation of its habitat by a hurricane.

Conservation and Recovery

The critical habitat of T. inabonensis is located within the Toro Negro Commonwealth Forest, which is managed by the Commonwealth Department of Natural Resources, Government of Puerto Rico. Apart from strict protection from any collection of specimens, the most important action needed to conserve the rare fern is to preserve its critical habitat. Provisions for its protection must be incorporated into the management plan for Toro Negro Commonwealth Forest. In addition, research should be conducted on its biology and habitat requirements, to provide knowledge for its management.


U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345

U. S. Fish and Wildlife Service
Boquerón Ecological Services Field Office
P. O. Box 491
Boquerón, Puerto Rico 00622-0491
Telephone: (787) 851-7297
Fax: (787) 851-7440


U. S. Fish and Wildlife Service. 2 July 1993. "Endangered and Threatened Wildlife and Plants: Determination of Endangered Status for Three Endemic Puerto Rican Ferns." Federal Register 58(126):35887-35891.

U. S. Fish and Wildlife Service. June, 1994. "U.S. Fish and Wildlife Service, Division of Endangered Species, Species Account: Three Endemic Puerto Rican Ferns." U. S. Fish and Wildlife Service, Endangered Species Program. ( (July 6, 2000).