Developmental and Structural Section
Rudall, Paula J. .
Homologies of floral structures in Pandanales.
The order Pandanales has recently been recircumscribed based on analyses of molecular sequence data, and now includes five families: Cyclanthaceae, Pandanaceae, Stemonaceae, Triuridaceae and Velloziaceae. This novel circumscription has prompted a reassessment of the wide range of reproductive structures in this order, some of them highly anomalous with respect to more typical monocot flowers. Questions to be addressed here include: (1) What constitutes a flower in this group? The flower-inflorescence boundary is often blurred. For example, the terminal floral unit in Sararanga has been interpreted as either a flower with a fleshy multicarpellate syncarpous superior ovary and reduced bract-like tepals, or a condensed fleshy inflorescence axis with numerous sunken perianthless flowers. Some other Pandanaceae lack a perianth entirely and have attractive, sugar-rich, sometimes fragrant bracts. Floral units of many Triuridaceae are difficult to fit into either category (inflorescence or flower), possessing features of both. For example, the "inside-out" floral unit of Lacandonia could be interpreted as either a single flower with three stamens surrounded by numerous free uniovulate carpels and a perianth, or a condensed inflorescence with tepal-like bracts, three (or possibly one terminal) perianthless male flowers and numerous reduced perianthless female flowers. (2) What is the evolutionary history of trimery, dimery and tetramery in Pandanales? Trimery is the most common condition in monocots, but floral units with four perianth parts and four stamens or staminodes occur in at least three families of Pandanales. (3) What are the relationships and synapomorphies within the newly-circumscribed Pandanales? Rigorous testing of the diverse floral characters in a morphological cladistic analysis is desirable but problematic, as floral homologies are difficult to interpret in this group. This paper presents morphological cladistic analyses coded according to contrasting hypotheses of floral structure.
1 - Royal Botanic Gardens, Kew, Jodrell Laboratory, Richmond, Surrey, TW9 3AB, UK
Presentation Type: Paper
Location: Alpine A (Snowbird Center)
Date: Monday, August 2nd, 2004
Time: 8:00 AM