A Hybrid of Gunnera from Costa Rica

Abstract

A study of a number of morphological characters confirms the pres- ence of a hybrid between the two species of Costa Rican Gunnnera, G. insignis and G. talamancana. Despite wind pollination and similar habitat preferences among all known species, hybrids of Gunnera are rare in nature because the disturbed sites they prefer are so small and labile. Road building, especially of the Pan-American Highway, has established large areas of more or less permanently disturbed habitat allowing the populations of the two different species to interdigitate and hybridize. Gunnera Linneaus is one of the most striking plants of the tropical American cloud forest. Although G. chilensis Lamarck has been a popular ornamental in Europe since before the last century, the systematics of the genus are very poorly understood. Both the gigantic size of its organs (two meter wide leaves, meter and a half long inflorescences), which make it so impressive, and its relatively inaccessible habitat in nature, lead to great difficulty in collecting. Most herbarium collections are quite fragmentary, which obscures and confuses the taxonomy (Biloni, 1959; Palkovic, 1978). I have had the opportunity to study Gunnera in Costa Rica on four different occasions, in 1970, 1971, 1972 and 1973 for the preparation of a study on the genecology, population dynamics and adaptive strategy of G. insignis (Oersted) A. de Candolle. I have become intimately familiar with most of the populations in the country and have studied their size, distribution and composition. There are two species of Gunnera in Costa Rica, G. insignis and G. talamancana Weber & Mora. Gunnera insignis is a wide-ranging giant herb extending from Panama to Nicaragua, found at elevations from perhaps 500 m to over 3400 m. As is characteristic of all species in its subgenus (Panke (Molina) Schindler), it has a solitary, thick, semi-erect stem (pachy- caul), which bears a terminal rosette of rounded, lobed leaves. It does not branch, except through injury, and bears axillary inflorescences. A single inflorescence may bear tens of thousands of tiny, wind-pollinated flowers, each producing a single, minute drupelet. Gunnera insignis is a colonizer of naturally disturbed sites, such as landslides and streambanks. Recently it has become a highly successful colonizer of road cuts, waste spills and other disturbances associated with road building. Construction of the Pan-American Highway opened the higher ele- vations of the Cordillera de Talamanca in the mid-1950's. Weber and Mora (1958) described a new species, G. talamancana, growing along the newly laid road on the crest of the cordillera. Despite its more restricted range, it colonizes disturbed habitats in much the same way as G. insignis.