Sabal causiarum, commonly known as the Puerto Rico palmetto or Puerto Rican hat palm, is a species of palm which is native to Hispaniola, Puerto Rico, the United States Virgin Islands, and the British Virgin Islands. As its common and scientific names suggest, its leaves are used in the manufacture of "straw" hats.
Stems: Solitary, massive, upright stems to 15 m tall and to 70 cm diameter. Leaf bases usually fall away quickly to leave a smooth gray stem with close rings. Leaves: Costapalmate, induplicate, twisted into several planes with a strongly arching costa, to 2 m wide. Leaf segments rigid, with numerous fibers along the segment margins. Petiole bases split. Flowers and fruits: Inflorescences exceeding the leaves in length, arching or pendulous, and branched to three orders. Flowers creamy white, bisexual. Ripe fruit black, spherical, 7-11 mm diameter.
Sabal causiarum is a fan palm with solitary, very stout stems, which grows up to 10 metres (33 ft) tall and 35–70 centimetres (14–28 in) in diameter. Plants have 20–30 leaves, each with 60–120 leaflets. The inflorescences, which are branched, arching or pendulous, and longer than the leaves, bear globose, black fruit. The fruit are 0.7–1.1 centimetres (0.3–0.4 in) in diameter; fruit size and shape are the main characteristics by which this species differs from Sabal domingensis.