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

Sieve-element plastids and rbc L nucleotide sequences were analysed for Velloziaceae and all families sometimes discussed as close allies (Acanthochlamydaceae, Amaryllidaceae, Bromeliaceae, Cyclanthaceae, Haemodoraccae, Hypoxidaceae, Pandauaccae, Pen-tastemonaceae, Stemonaceac). Velloziaceae (37 taxa investigated) contain sieve-element plastids defined here as subforms P2c a , P2c al P2c ap P2c al , f, and P2c ap f and distinct from those of any other monocotyledon by (1) angular crystals replacing to a large extent the monocot-specific cuneate crystals, (2) additional loosely-packed crystals, and (3) their very small average diameters. This sieve-element plastid syndrome is a synapomorphy of Velloziaceae and indicates the monophyly and early isolation of the family. Sieve-element plastids of the monotypic Acanthochlamydaceae share their small sizes with Velloziaceae, but all their crystals are cuneate, i.e. loosely-packed crystals were not found. Among the other families studied the sieve-element plastids of (a) some Bromeliaceae ( Ayensua in particular) contain loosely-packed crystals, (b) several Amaryllidaceae incorporate additional orthogonal crystals, and (c) Pandanaceae belong to form-Pef, but cuneate crystals are present throughout and the plastids are significantly larger than in Velloziaceae. The new information on the rbcL nucleotide sequences of 24 taxa of the Velloziaceae and of 20 additional taxa from putatively related families strongly support the monophyly of Velloziaceae and define Acanthochlamydaceae as its sister family. At the infra-familial level four evolutionary lines are discovered which correspond to major generic groups and their geographical distribution. The divergence time for the split between New Word and Old World taxa has been calculated as 40–70 million years, that between African and Madagascan species maximally 25 million years. The cladistic analysis requires that the monotypic genera Nanuza and Talbotia be included within Vellozia and Xerophyta , respectively. At the ordinal level the analysis of the rbc L-data strengthens the Pandanales as a monophyletic clade.