The evolution of morphological novelties and bauplan oddities in flowering plants with special emphasis on African river-weeds (Podostemaceae)
Fuzzy morphology – including continuum and process morphology sensu Agnes Arber and Rolf Sattler – becomes fashionable among developmental and evolutionary biologists, interested in the evolution of developmental pathways of flowering and other vascular plants (Rutishauser & Isler 2001, Kirchoff et al. 2008, Rutishauser et al. 2008). Unlike classical (i.e. crisp) plant morphology, fuzzy morphology allows interpreting plant structures as category A as well as category B, or as A – B intermediates. We focus on flowering plants where the usual bauplans are transcended or blurred to some degree. These plants are called morphological misfits. They have evolved forms that do not clearly fit into the classical root-shoot model (CRS model). Thus, our role is to provide the developmental basis for a better understanding of odd bauplans, incorporating new ideas from evolutionary developmental biology (“evo-devo”). How did morphological misfits (idiosyncrasies) evolve in Podostemaceae, Lentibulariaceae, and other flowering plants, based on molecular phylogenies? We already explored morphological novelties and bauplan oddities of Podostemaceae (river-weeds), Lentibulariaceae (bladderwords & allies), Nymphaeaceae (water-lilies) and other flowering plants. For example, are the green flattened roots of Podostemaceae (river-weeds) really “roots”? What exactly happens when leaf primordia are replaced by floral buds (e.g. in Nymphaea & Co.), or when floral buds are replaced by shoot apical meristems (as observable in Nymphaea prolifera, Grob et al. 2006)? Our comparative morphological analyses resulted in an essay and a book chapter for a general audience interested in the evolution of developmental pathways (Rutishauser & Moline 2005; Rutishauser et al. 2008). Evolutionary questions here included are: How robust vs. fragile are bauplans (including branching patterns, phyllotaxy) in vascular plants? Are plants and their parts used to having identity crises? How to define the various levels of homology in times of developmental genetics? In collaboration with Dr. Alex Bernhard (same Institute) we created an e-learning unit on pattern formation in vascular plants, especially phyllotaxis (Bernhard et al. 2004). Only a thorough morphological knowledge of flowering plants with bauplan oddities will help better understanding the construction modes of more typical vascular plants.
A special focus of our research project is on African Podostemaceae, but we also do comparative studies on American and Asian taxa. There are 16 genera and c. 85 species of Podostemaceae-Podostemoideae known in Africa and Madagascar. Cameroon with nine genera and 35 species is the Eldorado for Podostemaceae research! Most of them are restricted to a single river or waterfall only. Several of these taxa may be the products of poor taxonomic understanding in spite of the valuable contributions mainly by Colette Cusset (Paris) and Hans Hess (Zurich). In collaboration with African botanists we have organized symposia on Podostemaceae in Vienna (Austria 2005) and Yaoundé (Cameroon 2007) with contributions from Cameroon, Ghana, U.S.A., Japan, Germany, and Switzerland. Moreover, we explore the wealth of African Podostemaceae in the field (especially in Cameroon). There is ongoing collaboration with dipl. Bot. Jean-Paul Ghogue (Cameroon), Dr. Gabriel Ameka (Ghana), Dr. Claudia Bove (Brazil), Dr. Satoshi Koi (Japan), Dr. Masahiro Kato (Japan) and Dr. Tom Philbrick (U.S.A.). Comparative morphological studies and molecular analyses are published (e.g. Moline et al. 2006, 2007, Thiv et al. 2009, Ruhfel et al. 2011, Koi et al. 2012) see also website www.systbot.uzh.ch/static/podostemaceae). Badly known and newly discovered taxa are described (Ghogue et al. 2009, Kita et al. 2008, Koi et al. 2009, Pfeifer et al. 2009). These results indicate that the taxonomy of African Podostemaceae-Podostemoideae is in need of revision. Awareness of the peculiar architectural rules in Podostemaceae may also help to protect some of these highly endangered taxa and their fragile habitats. They show various morphological oddities (key innovations) not known from other flowering plants, e.g. flattened green roots, endogenous formation of flowers and shoots arising from stem cortex, flowers arising from leaves (epiphylly), and leaves giving rise to daughter shoots on both abaxial and adaxial side of their bases. We still need more thorough morphological and developmental analyses which are based on microtome sections and scanning electron microscopy. – The Institute of Systematic Botany (University of Zurich) is an excellent place to do comparative and developmental morphology besides molecular and traditional systematics including herbarium work.
Key Words: comparative morphology, developmental patterns, evo-devo, molecular systematics, morphological misfits, phyllotaxis, systematic botany; Lentibulariaceae, Podostemaceae.