Tectaria estremerana

Tectaria estremerana is a rare species of fern known by the common name Puerto Rico halberd fern. It is endemic to Puerto Rico. It is a federally listed endangered species of the United States.

This fern has fronds up to 80 cm long, each with a hairy, orange brown stipe. The rachis 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. The ferns are located about 200 m away from the Arecibo Radio Telescope. Later more individuals were discovered in Río Abajo Commonwealth Forest and in the municipality of Florida.