Tectaria estremerana is a rare species of fern

Fern

A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...

 known by the common name Puerto Rico halberd fern. It is endemic to Puerto Rico

Puerto Rico

Puerto Rico , officially the Commonwealth of Puerto Rico , is an unincorporated territory of the United States, located in the northeastern Caribbean, east of the Dominican Republic and west of both the United States Virgin Islands and the British Virgin Islands.Puerto Rico comprises an...

. It is a federally listed endangered species

Endangered species

An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...

 of the United States.

This fern has fronds up to 80 centimeters long, each with a hairy, orange brown stipe

Stipe (botany)

In botany, a stipe is a stalk that supports some other structure. The precise meaning is different depending on which taxonomic group is being described....

. The rachis

Rachis

Rachis is a biological term for a main axis or "shaft".-In zoology:In vertebrates a rachis can refer to the series of articulated vertebrae, which encase the spinal cord. In this case the rachis usually form the supporting axis of the body and is then called the spine or vertebral column...

 is hairy and the leaf is divided into a few elongated leaflets.

When this plant was placed on the United States' Endangered Species List it was known from a population of 23 individuals in Arecibo, Puerto Rico

Arecibo, Puerto Rico

Arecibo is a municipality in the northern midwest coast of Puerto Rico and located by the Atlantic Ocean, north of Utuado and Ciales; east of Hatillo; and west of Barceloneta, and Florida. Arecibo is spread over 18 wards and Arecibo Pueblo...

. The ferns are located about 200 meters away from the Arecibo Radio Telescope

Arecibo Observatory

The Arecibo Observatory is a radio telescope near the city of Arecibo in Puerto Rico. It is operated by SRI International under cooperative agreement with the National Science Foundation...

. Later more individuals were discovered in Río Abajo Commonwealth Forest and in the municipality of Florida

Florida, Puerto Rico

Florida is a municipality of Puerto Rico located north of Ciales, south of Barceloneta, east of Arecibo, and west of Manatí. Florida is spread over one ward and Florida Pueblo...

.