The Bromeliaceae

Pineapple belongs to the order Bromeliales, family Bromeliaceae, subfamily Bromelioideae. With 2794 species among 56 genera, according to Luther and Sieff (1998), this is the largest family whose natural distribution is restricted to the New World, with the exception of Pitcairnia feliciana (Aug. Chev.) Harms & Mildbr., which is native to Guinea. Their unified geographical distribution and their strong adaptation towards an epiphytic mode of life indicate that this is quite a young family. On the other hand, morphologically they seem older than Rapateaceae, which led Smith (1934) to accept that their restriction to the Americas does not indicate extreme youth. Judd et al. (1999) consider that the family probably represents an early divergent clade within the superorder Commelinanae. The Bromeliaceae have adapted to a very wide range of habitats, ranging from terrestrial to epiphytic, deep shade to full sun, mesic to extremely xeric and sea level to alpine, and from the hot and humid tropics to the cold and dry subtropics. They thus cover a wide area, from the centre of the USA to the northern regions of Argentina and Chile (Smith, 1934). The Bromeliaceae are set apart from other monocots by the unique, stellate or scale-like multicellular hairs and the unusual conduplicate, spiral stigmas (Gilmartin and Brown, 1987). They are also characterized by a short stem, a rosette of narrow stiff leaves, terminal inflorescences in the form of racemes or panicles, hermaphroditic and actinomorphic trimerous flowers with well-differentiated calyx and corolla, six stamens and superior to inferior trilocular ovary, with axile placentation and numerous ovules. Fruits are capsules or berries and contain small naked, winged or plumose seeds, with a reduced endosperm and a small embryo. Most species are epiphytic or saxicolous, but some are terrestrial. They are particularly adapted to water economy, based on: (i) rosette structure; (ii) ability to absorb water and nutrients through their waxy leaves and aerial roots; (iii) ability to store water in specialized aquiferous leaf tissue; (iv) multicellu-lar trichomes functioning as water valvulae and reflecting radiation; (v) a thick cuticle; (vi) location of stomates in furrows, limiting evapotranspiration; and (vii) CAM. Their root system is not well developed and functions mostly to anchor the plant.

The Bromeliaceae are divided into three subfamilies, the Pitcarnioideae, the Tillandsioideae and the Bromelioideae. While this division is widely recognized, their phy-logenetic study has been confounded by high levels of homoplasy for morphological and ecological characters. Most experts agree that certain attributes have arisen several times independently as adaptations to their extreme environment. Molecular studies have given contradictory results, placing different subfamilies at the base of the Bromeliaceae (Clark and Clegg, 1990; Givnish et al, 1990; Ranker et al., 1990; Terry et al, 1997). The Pitcarnioideae were long held to be the most archaic. They are almost terrestrial, with armed leaf margins, hypogenous or epygenous flowers and dry dehiscent cap sules containing naked or appendaged seeds adapted to wind dispersal. Their monophyly is now questioned and new subfamilies could be defined (Ranker et al., 1990; Terry et al., 1997). The subfamilies Tillandsioideae and Bromelioideae are considered monophyletic. The former include mostly epiphytic species, with smooth leaf margins, flowers usually hypogenous and dry dehiscent capsules containing many plumose seeds adapted to wind dispersal. The second is the most numerous. Most Bromelioideae are epiphytic, frequently spiny, with epigynous flowers and fleshy or leathery berries containing naked seeds as an adaptation to dispersion by birds or mammals. All the species examined exhibit CAM, with the exception of those of the genus Greigia, a trait much less frequent in the other subfamilies (Medina, 1990). They seem to have evolved from eastern Brazil and the Amazon basin, and they show a tendency to fusion of parts, fusion of their carpels to make an indehiscent fruit, formation of an inferior ovary and fusion of sepals, petals and filaments. As stated by Smith (1934), 'Ananas capped the fusion tendency by merging the whole inflorescence, flowers, bracts and all into one massy compound fruit.'

Pineapple is by far the most important economic plant in the Bromeliaceae. However, in the same Bromelioideae subfamily, some Aechmea and Bromelia species also yield edible fruits, such as A. bracteata (Swartz) Grisebach, A. kuntzeana Mez, A. longifolia (Rudge) L.B. Smith & M.A. Spencer, A. nudi-caulis (L.) Grisebach, B. antiacantha Bertoloni, B. balansae Mez, B. chrysantha Jacquin, B. karatas L., B. hemisphaerica Lamarck, B. nidus-puellae (André) André ex. Mez, B. pinguin L., B. plumieri (E. Morren) L.B. Smith and B. tri-anae Mez (Rios and Khan, 1998). The most common are known and consumed locally, under names like cardo or banana-do-mato (bush banana), piñuelas (small pineapple) or karatas, gravatá and croata (derived from Amerindian names given to terrestrial bromeliads). Many other bromeliads are cultivated as ornamentals, gathered for fibre extraction or used in traditional medicine (Corrêa, 1952; Purseglove, 1972; Reitz, 1983; Rios and Khan, 1998).

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