The ultramafic flora of the Santa Elena peninsula, Costa Rica: A biogeochemical reconnaissance

The Santa Elena peninsula in the northwest of Costa Rica protrudes about 30 km westwards into the Pacific Ocean, and measures about 8–16 km in a north–south direction. Several geological studies have been carried out since 1953, showing that much of the peninsula is made up of peridotite, cut by mafic dykes. Only one previous brief examination appears to have been made of the vegetation in relation to the composition of the soils. We present here the results of a survey of some soils and plants of the eastern part of the peridotite massif, in which 73 plant specimens representing 51 identified species were collected and analyzed. The soils sampled all showed extreme ultramafic characteristics: Fe 10–16%, Mg 4–16%, Ca 0.5–1.4%; Ni 3000–7500 mg/kg, Cr 1400–3650 mg/kg, Co 150–325 mg/kg. The plants collected include several from genera such as Arrabidaea, Chamaesyce, Helicteres, Hyptis, Lippia, Oxalis, Polygala, Turnera and Waltheria that are also represented on ultramafics elsewhere in the Americas (e.g. Cuba, Puerto Rico, Brazil). Few of the species appear to be endemic to Costa Rica or to the ultramafics of Santa Elena. None of the specimens collected exhibited hyperaccumulation of nickel, the highest Ni concentration being 275 mg/kg in Buchnera pusilla.