Ecological patterns in the Bromeliaceae of the lomas formations of CoastalChile and Peru

Studies of geographic distribution and physiological adaptations in the Bro meliaceae of coastal Chile and Peru provide insights into the ecological pa tterns of habit selection and speciation. The hyperarid coastal Atacama and Peruvian Deserts along the Pacific coast of South America contain a surpri singly rich flora of bromeliad species. These include representatives of al l three Bromeliaceae subfamilies: two terrestrial Bromelioideae and two ter restial Pitcairnioideae, all with rooted growth morphologies, and 14 specie s of Tillandsioideae (all Tillandsia) with epiphytic and unrooted, terrestr aial representatives. The Bromelioideae are represented by two species of P uya MOLINA, one each in Peru and Chile. The Pitcairnioideae are represented by two genera, Deuterocohnia and Pitcairnia, with one species each. The 14 Tillandsia species are distributed in five subgenera which have successful ly invaded the coastal deserts, and include both widespread and local endem ics with xeromorphic adaptations. All the Tillandsia species are epiphytic in the broad sense, but in addition to growing on plants, they are found gr owing on rocks (i.e. saxicolous or epilithic). Six species (T. purpurea,;T: latifolia, T. capillaris, T. marconae, T. werdermanii, and T. landbeckii) have evolved a highly specialized substrate ecology where they grow essenti ally unrooted on sand (i.e. epiarenic). Nowhere in the world are bromeliads more dominant or have more biomass than in these coastal species growing o n sand. Many of these species grow at the absolute limits of vascular plant tolerance, with the entire community consisting of a single Tillandsia spe cies. Rooted, terrestrial bromeliads in the coastal lomas formations tall P itcairnioideae) include CAM, C-3, and C-3-CAM flexible taxa in their metabo lic systems, the CAM species growing in the most arid sites along the coast and C3 species growing in the most mesic habitats within the center of the coastal fog belt where fog moisture input is highest. All of the epiphytic Tillandsia species of the coastal desert region utilize CAM metabolism ent irely or in part. At least two species, 7 latifolia and 7 tragophoba, utili ze a flexible C3-CAM mode of carbon fixation. Whereas most of the desert-in habiting Tillandsia species have relatively narrow leaves covered by water absorbing trichomes on their surface, T: multiflora in northern Peru and 7 tragophoba in northern Chile are tank-forming species where the bases of th e leaves form a water-containing reservoir. The occurrence of the latter as a local endemic in hyperarid northern Chile is remarkable since it occurs thousands of kilometers south of its closest potential relatives in the cen tral Andes.