In the Cactaceae the

Posted by Ellie on Dec 26, 2008 in Evolution and Phylogeny | 0 comments

In the Cactaceae, the process of developing phylogenetic scheme rarely identifies clear definable groups, as the descriptions of many genera and species of cactus are incomplete. They have no leaves and no glochids and the flowers are usually funnel shaped. When water is scarce the folds sink in between the ribs and when water is plentiful the folds swell out. Seedlings bear fleshy cotyledons. This ancestor was the first to evolve the Areole, the specialized Axillary Bud, unique to and very important definer of the Cactaceae.

Seedlings possess fleshy cotyledons similar to those of the Pereskiae. godsefiana, Lemon Vine, hardy woody shrub with succulent leaves which produces the delicious Barbados Gooseberry, is thought to resemble the ancestor closely. SubFamily Pereskioideae Of the two genera, Pereskia and Maihuena, forming this primitive subfamily, the Pereskiae are genus of about species of jungle trees, vines and shrubs native to Central America and the Indies. American epiphytes familiar as the Holiday, Orchid, and Mistletoe cacti among others. The extent of cactus variation and geographical distribution is insufficiently known due to the poor fossil record.

The last two are epiphytic, tree or cliffdwelling jungle cacti. Maihuena, the second genus, is mound forming, low plant. There are over thousand species showing wide range of morphological diversity. The cotyledons of the Cactoideae members are microscopic in the seed and unlike the Pereskiae and Opuntiae, they do not enlarge in proportion to the growing embryo. Group contains certain Carribean genera descended from Pereskia which first developed columnar morphology as thin stemmed, erect and creeping types. By this time, Plate Tectonics had spread the Atlantic sea floor to such width that these adaptations were absolutely confined to the Americas.

They have no leaves and no glochids and the flowers are usually funnel shaped.

Group IV comprises the spherical and columnar cacti of South America which are more or less similar at either extreme. Its descendants diversified, bit by bit, as each evolved successful survival responses to changing conditions in its own habitat.

Group III consists of the MexicanNo. They have no leaves and no glochids and the flowers are usually funnel shaped. Genealogical Tree of the Family Cactaceae Adapted from Barthlott, 1979 There are over species of cacti, and these can be arranged in system based on their presumed degrees of relationship.