Systematics and evolution of Velloziaceae, with special reference to sieve-element plastids and rbcL sequence data

Sieve-element plastids and rbcL nucleotide sequences were analysed for Vell oziaceae and all families sometimes discussed as close allies (Acanthochlam ydaceae, Amaryllidaceae, Bromeliaceae, Cyclanthaceae, Haemodoraceae, Hypoxi daceae, Pandanaceae, Pentastemonaceae, Stemonaceae). Velloziaceae (37 taxa investigated) contain sieve-element plastids defined here as subforms P2c(a -c), P2c(al), P2c(ap), P2c(al)f, and P2c(ap)f and distinct from those of an y other monocotyledon by (1) angular crystals replacing to a large extent t he monocot-specific cuneate crystals, (2) additional loosely-packed crystal s, and (3) their very small average diameters. This sieve-element plastid s yndrome is a synapomorphy of Velloziaceae and indicates the monophyly and e arly isolation of the family. Sieve-element plastids of the monotypic Acant hochlamydaceae share their small sizes with Velloziaceae. but all their cry stals are cuneate, i.e. loosely-packed crystals were not found, Among the o ther families studied the sieve-element plastids of (a) some Bromeliaceae ( Ayensua in particular) contain loosely-packed crystals, (b) several Amaryll idaceae incorporate additional orthogonal crystals, and (c) Pandanaceae bel ong to form-Pef, but cuneate crystals are present throughout and thr plasti ds are significantly larger than in Velloziaceae. The new information on th e rbcL nucleotide sequences of 24 taxa of the Velloziaceae and of 20 additi onal taxa from putatively related families strongly support the monopoly ly of Velloziaceae and define Acanthochlamydaceae as its sister family. At th e infra-familial level four evolutionary lines are discovered which corresp ond re, major generic groups and their geographical distribution. Thr diver gence time for the split between New Word and Old World taxa has been calcu lated as 40-70 million years. that between African and Madagascan species m aximally 25 million years. The cladistic analysis requires that the monotyp ic genera Nanuza and Talbotia be included within Vellozia and Xerophyta, re spectively. At the ordinary level the analysis of the rbl l-data strengthen s the Pandanales as a monophyletic clade. (C) 2000 The Linnean Society of L ondon.