Evolution, Diversity, and Habitats of Poikilohydrous Vascular Plants
Water stress is a common environmental constraint in terrestrial ecosystems. Among the various strategies to cope with temporal lack of water, poikilohydry is an important adaptive trait under specific habitat conditions. Desiccation tolerant vascular plants are particularly common among ferns, fern allies, and angiosperms that colonize forest canopies and mainly tropical rock outcrops (e.g., granitic/gneissic inselbergs, ferricretes) where environmental conditions (e.g., high temperatures, lack of water, and soil) are harsh.
Within vascular plants poikilohydry has evolved more than a dozen times independently. Within angiosperms desiccation tolerance is absent in the basalmost angiosperm clades and has evolved in rather advanced lineages. Most species rich are ferns and fern allies (e.g., Hymenophyllaceae, Polypodiaceae, Selaginellaceae) with angiosperms (monocotyledons: Boryaceae, Cyperaceae, Poaceae, Velloziaceae; dicotyledons: e.g., Gesneriaceae, Linderniaceae, Myrothamnaceae) playing only a minor role. It can be speculated that a number of Bromeliaceae could be poikilohydrous too. The total number of desiccation tolerant vascular plant species could reach c. 1,300 (c. 1,000 ferns/fern allies, c. 300 angiosperms).
In particular, on tropical rock outcrops, desiccation-tolerant vascular plants may become dominant. Particularly characteristic are mat-forming monocotyledons that cover steep rocky slopes whereas other desiccation tolerant vascular plants occur in crevices, shallow depressions, and temporally water-filled rock pools. Prominent mat-formers on inselbergs in South America, Africa, and Madagascar are treelet-like Cyperaceae and Velloziaceae that can attain an age of several hundred years. Their stems mainly consist of adventitious roots that possess a velamen radicum that might contribute to the rapid uptake of water.
Desiccation tolerant vascular plants are most richly represented in constantly wet to seasonally dry (length of the dry season 3–8 months) tropical regions with their species numbers decreasing under desert-like climatic conditions. Centres of diversity for resurrection plants are certain tropical regions with East Africa, Madagascar, and southeastern Brazil being most speciose. In the temperate zone parts of Australia and North America are likewise rich in poikilohydric species.
Increasing human pressure (e.g., fire, quarrying) on the natural habitats of poikilohydric vascular plants is a serious threat to their long-term survival and measures for their ex situ conservation should be taken into account.
KeywordsVascular Plant Desiccation Tolerance Rock Outcrop Resurrection Plant Rocky Slope
Financial support is gratefully acknowledged for rock outcrop studies by the Deutsche Forschungsgemeinschaft. The author is deeply indebted for valuable discussions and remarks to W. Barthlott (Bonn), J.-P. Ghogue (Yaoundé), S. D. Hopper (Kew), N. Korte (Rostock), Z. Tuba (Gödöllö) and G. Zotz (Oldenburg).
- Dinter K (1918) Botanische Reisen in Deutsch-Südwest-Afrika. Feddes Rep Beih 3:1–169Google Scholar
- Fahn A, Cutler DF (1992) Xerophytes. In: Braun HJ, Carlquist S, Ozenda P, Roth I (eds) Handbuch der Pflanzenanatomie, vol 13, part 3, Spezieller Teil. Borntraeger, BerlinGoogle Scholar
- Gaff DF (1981) The biology of resurrection plants. In: Pate JS, McComb AJ (eds) The biology of Australian plants. University of Western Australia Press, Perth, pp 114–146Google Scholar
- Gaff DF (1989) Responses of desiccation tolerant “resurrection” plants to water stress. In: Kreeb KH, Richter H, Hinckley TM (eds) Structural and functional responses to environmental stresses: water shortages. SPB Academic Publishing, The Hague, pp 264–311Google Scholar
- Hartung W, Schiller P, Dietz K-J (1998) The physiology of poikilohydric plants. Prog Bot 59:299–327Google Scholar
- Heil H (1924) Chamaegigas intrepidus Dtr., eine neue Auferstehungspflanze. Beitr Bot Zentralbl 41:41–50Google Scholar
- Kappen L, Valladares F (2007) Opportunistic growth and desiccation tolerance: the ecological success of poikilohydrous autotrophs. In: Pugnaire F, Valladares F (eds) Functional plant ecology, 2nd edn. CRC/Taylor and Francis Group, Boca Raton/London, pp 7–65Google Scholar
- Kluge M, Brulfert J (2000) Ecophysiology of vascular plants on inselbergs. In: Porembski S, Barthlott W (eds) Inselbergs: biotic diversity of isolated rock outcrops in tropical and temperate regions, vol 146, Ecological Studies. Springer, Berlin, pp 143–174Google Scholar
- Kornás J (1977) Life-forms and seasonal patterns in the pteridophytes of Zambia. Acta Soc Bot Pol 46:669–690Google Scholar
- Nitta JH (2006) Distribution, ecology and systematics of the filmy ferns (Hymenophyllaceae) of Moorea (French Polynesia). University of California, Department of Integrative Biology, Berkeley, CAGoogle Scholar
- Porembski S (2006) Vegetative architecture of desiccation-tolerant arborescent monocotyledons. Aliso 22:129–134Google Scholar
- Porembski S, Barthlott W (eds) (2000) Inselbergs: biotic diversity of isolated rock outcrops in tropical and temperate regions, vol 146, Ecological studies. Springer, BerlinGoogle Scholar
- Sazima M, Sazima I (1990) Humming bird pollination in two species of Vellozia (Liliiflorae, Velloziaceae) in southeastern Brazil. Bot Acta 103:83–86Google Scholar
- Schiller P, Wolf R, Hartung W (1999) A scanning electron microscopical study of hydrated and desiccated submerged leaves of the aquatic resurrection plant Chamaegigas intrepidus. Flora 194:97–102Google Scholar
- Szarzynski J (2000) Xeric islands. Environmental conditions on inselbergs. In: Porembski S, Barthlott W (eds) Inselbergs: biotic diversity of isolated rock outcrops in tropical and temperate regions, vol 146, Ecological Studies, Springer, Berlin, pp 37–48Google Scholar
- Walter H (1931) Die Hydratur der Pflanze und ihre physiologisch-ökologische Bedeutung. Gustav Fischer, JenaGoogle Scholar
- Weber A (2004) Gesneriaceae. In: Kadereit JW (ed) The families and genera of vascular plants, vol 7, Flowering plants, dicotyledons: Lamiales (except Acanthaceae including Avicenniaceae). Springer, BerlinGoogle Scholar
- Zotz G, Andrade J-L (1998) Water relations of two co-occurring epiphytic bromeliads. J Plant Physiol 152:545–554Google Scholar