Roystonea is a genus of eleven species of monoecious palms, native to the Caribbean Islands, and the adjacent coasts of the United States (Florida), Central America and northern South America.[3][4][5] Commonly known as the royal palms, the genus was named after Roy Stone, a U.S. Army engineer. It contains some of the most recognizable and commonly cultivated palms in tropical and subtropical regions.
Roystonea is a genus of large, unarmed, single-stemmed palms with pinnate leaves. The large stature and striking appearance of a Roystonea palm makes it a notable aspect of the landscape. The stems, which were compared to stone columns by Louis and Elizabeth Agassiz in 1868, are smooth and columnar, although the trunks of R. altissima and R. maisiana are more slender than those of typical royal palms. Stems often are swollen and bulging along portions of their length, which may reflect years where growing conditions were better or worse than average. Leaf scars are often prominent along the stem, especially in young, rapidly growing individuals. Stem color ranges from gray-white to gray-brown except in R. violacea, which have violet-brown or mauve stems. Royal palm, R. oleracea, reaches heights of 42 metres (138 ft), but most species are in the 15 to 20 m (49 to 66 ft) range.[6] The largest Royal palm is located in Floresta Estadual Edmundo Navarro de Andrade in Rio Claro, São Paulo, Brazil with 42.4 m and was discovered by Vincent Ferh and Mauro Galetti
Roystonea leaves consist of a sheathing leaf base, a petiole, and a rachis. The leaf base forms a distinctive green sheath around the uppermost portion of the trunk. Known as the crownshaft, this sheath extends 1.4–2 metres (4 ft 7 in – 6 ft 7 in) down the trunk. The petiole connects the lead base with the rachis. Zona only reported petiole lengths for three of the 10 species, ranging from 20 to 100 centimetres (8 to 39 in). The rachis is pinnately divided and ranges from 3.2 to 5.8 m (10 to 19 ft) long. The leaf segments themselves range in length from 60 to 79 cm (24 to 31 in) in R. altissima up to as much as 132 cm (52 in) in R. lenis. They are arranged in two or three planes along the rachis. Many authors have reported that the leaves R. oleracea are arranged in a single plane, but American botanist Scott Zona reported that this is not the case.[6]
These plants have the ability to easily release their leaves in strong winds, a supposed adaption serving to prevent toppling during hurricanes. Inflorescences occur beneath the crownshaft, emerging from a narrow, horn-shaped bract. The flowers on the branched panicles are usually white, unisexual, and contain both sexes. The fruit is an oblong or globose drupe 1–2 centimetres (0.39–0.79 in) long and deep purple when ripe.[7] Some species so closely resemble one another that scientific differentiation is by inflorescence detail; flower size, colour, etc.
Roystonea is placed in the subfamily Arecoideae and the tribe Roystoneae,[8] which only contains Roystonea.[9] The placement of Roystonea within the Arecoideae is uncertain; a phylogeny based on plastid DNA failed to resolve the position of the genus within the Arecoideae.[10] As of 2008, there appear to be no molecular phylogenetic studies of Roystonea.[8] One species is known only from two fossilized flowers preserved in Dominican amber which were described in 2002.[11]
Roystonea has a circum-Caribbean distribution which ranges from southern Florida in the north, to southern Mexico, Honduras and Nicaragua in the east and Venezuela and Colombia in the south. Species are found throughout the Caribbean, although only Jamaica and Hispaniola (with two native species) and Cuba (with five native species) have more than one native species. A few species are planted in Tunisia as well.[6]