Hatillo is a town and municipality located in Puerto Rico's north coast, bordered by the Atlantic Ocean to the north, Lares and Utuado to the south, Camuy to the west, and Arecibo to the east. According to the 2000 US Census Hatillo is spread over nine barrios and Hatillo Pueblo. It is part of the San Juan-Caguas-Guaynabo Metropolitan Statistical Area.
Leptocereus grantianus (sebucan) is a sprawling or suberect, nearly spineless cactus, reaching up to 2 meters in height and 3 to 5 centimeters in diameter. Its elongated stems have from three to five prominent ribs with broadly scalloped edges. Ribs of young joints are thin, and the small areoles or spine-bearing areas may bear from one to three minute, nearly black spines which disappear as the joints grow older. The flowers are solitary at terminal areoles, from 3 to 6 centimeters long, and nocturnal. The outer perianth segments are linear, green, and tipped by an areole like those of the tube and ovary. The inner perianth segments are numerous, cream-colored, oblong-obvate, obtuse, and about 8 millimeters long. The fruit is subglobose to ellipsoid and about 4 centimeters in diameter.
Auerodendron pauciflorum is a rare species of flowering plant in the family Rhamnaceae. One English language common name is turtlefat. It is endemic to Puerto Rico, where it is known from only one population in Isabela. At the time the plant was federally listed as an endangered species by the United States in 1994, only ten individual plants were known to exist. By 1997, there were 19 known specimens.
Pleodendron macranthum (chupacallos) is a rare species of tree in the family Canellaceae. It is endemic to Puerto Rico, where there are only three tiny populations remaining. Two individual plants are located in El Yunque and 8 to 10 plants remain in Río Abajo State Forest. This tree is a federally listed endangered species of the United States.
Schoepfia arenaria is an extremely rare species of hemiparasitic flowering plant in the Schoepfiaceae family. It grows as a small, multi-trunked tree. It is endemic to Puerto Rico, where it is found growing along the northern coast. A local Spanish vernacular name recorded for this tree is araña ('spider'). It has no common name in English.
Styrax portoricensis, locally known as palo de jazmin, is a species of flowering plant in the family Styracaceae. It is endemic to Puerto Rico. It is one of the rarest endemic trees of Puerto Rico and is known to occur only in the northeastern Luquillo Mountains and the north-central Cayey Mountains.
Thelypteris is a genus of ferns in the subfamily Thelypteridoideae, family Thelypteridaceae, order Polypodiales. Two radically different circumscriptions of the genus are in use as of January 2020. In the Pteridophyte Phylogeny Group classification of 2016, the genus is a very small one with about two species. In other approaches, the genus is the only one in the subfamily Thelypteridoideae, and so includes between 875 and 1083 species.
Amauropelta noveboracensis, the New York fern, is a perennial species of fern found throughout the eastern United States and Canada, from Louisiana to Newfoundland, but most concentrated within Appalachia and the Atlantic Northeast. New York ferns often forms spreading colonies within the forests they inhabit.
Adenophorus periens is a rare species of fern known by the common name pendant kihi fern. It is endemic to Hawaii, where it is known from one population in Puna on the island of Hawaii and a few occurrences on Kauai and Molokai. The fern occurs in wet mountain forests on volcanic slopes. It grows on trees. There are perhaps 2000 individual plants remaining. This is a federally listed endangered species of the United States.
Adiantum vivesii is a rare species of maidenhair fern known by the common name Puerto Rico maidenhair.
Aristida portoricensis is a rare species of grass known by the common name pelos del diablo. It is endemic to Puerto Rico, where it is known from two locations, one in a residential area of Mayagüez and one in the Sierra Bermeja. Two other known sites have been extirpated by development of the habitat. It is a federally listed endangered species of the United States.
Cranichis ricartii is a rare species of orchid known by the common name Puerto Rico helmet orchid. It is native to Puerto Rico, where it is known from three locations in one forest. The plant has also been seen in Guadeloupe. The plant's rarity is the main reason for its listing as an endangered species of the United States.
Daphnopsis hellerana is a rare species of flowering plant in the genus Daphnopsis of the family Thymelaeaceae. It is endemic to Puerto Rico, where there were only four populations remaining in 1992, with a total of 125 individuals. It was federally listed as an endangered species of the United States in 1988.
Elaphoglossum serpens is a rare species of fern that grows only on Cerro de Punta, the highest mountain in Puerto Rico. The fern grows at one location, where there are 22 known specimens. It was federally listed as an endangered species of the United States in 1993.
Mitracarpus maxwelliae is a rare species of flowering plant in the coffee family known by the common name Maxwell's girdlepod. It is endemic to Puerto Rico, where it is known only from the Guánica Commonwealth Forest in Guánica. It grows in only one location in a coastal scrub forest and dwarf forest with limestone gravel substrates. Other plants in the habitat include Bucida buceras, Bursera simaruba, Exostema caribaeum, Coccoloba microstachya, Plumeria alba, and Pilosocereus royenii.
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.
Amauropelta inabonensis, synonym Thelypteris inabonensis, is a rare species of fern known by the common name cordillera maiden fern. It is endemic to Puerto Rico, where it is known from only two localities: at the headwaters of Río Inabón and at the Toro Negro State Forest. It is a federally listed endangered species of the United States.
Goniopteris yaucoensis, synonym Thelypteris yaucoensis, is a rare species of fern known by the common name Puerto Rico maiden fern. It is endemic to Puerto Rico, where it is known from only three localities. It is a federally listed endangered species of the United States.
Vernonia proctorii is a rare species of flowering plant in the aster family known by the common name Proctor's ironweed. It is endemic to Puerto Rico, where there are two populations. It is threatened by the destruction of its habitat. It is a federally listed endangered species of the United States.
