The bryophytes include three major groups: the liverworts, mosses and hornworts. They are the second largest group of land plants (embryophytes), exceeded only by the flowering plants. Bryophytes are found on every continent and landmass, including Antarctica, and occupy remarkably diverse environments, from deserts to fresh water. Bryophytes have a key position in land plant evolution being the closest living relatives of the first land plants.
I am interested in diverse aspects of bryophyte biology including physiology, cell biology and development, reproductive biology and ecology all variously interrelated to their systematics and phylogeny. I variously collaborate on a range of projects with Jeffrey G. Duckett (NHM); Howard Matcham (NHM); Martin Bidartondo (Kew Gardens/UCL); Karen Renzaglia (Southern Illinois University); Roberto Ligrone (Seconda Universita’ di Napoli); Christ Cargill (Australian National Herbarium); and with conservation agencies.
Habrodon perpusillus - gemmiferous protonemata © S. Pressel
The evaluation of and search for novel morphological characters in interpreting bryophyte phylogeny, including protonema morphology in mosses and thallus surface ornamentation and gemma formation in hornworts. Protonemal developmental studies (including the production and liberation mechanisms of protonemal asexual propagules) are providing novel ontogenetic data that raise new phylogenetic hypotheses that either support or challenge those derived from molecular studies. This work is also providing important new insights into the roles of asexual propagules in the ecology and reproductive biology of mosses, especially in those taxa where sexual reproduction is not known.
Understanding the development and functional significance of characters used in systematics. Another exciting line of research involves the analysis of characters widely used in moss systematics but whose development and functional significance remain to be elucidated e.g. leaf papillae and peristome ornamentation. An understanding of the interrelationships between structure and function in these characters provides a new basis for evaluating directions of evolution and hence resolving major questions in moss phylogeny.
Rhynchostegium confertum - peristome © S. Pressel
Desiccation biology of bryophytes. Bryophytes, the earliest diverging living clades of land plants, have retained the poikilohydry and vegetative desiccation tolerance characteristic of the first land-invading plants. As well as maintaining a strong interest in the desiccation biology of gametophytic tissues I have recently turned my attention to that of the sporophyte generation and in particular to the function of stomata in mosses and hornworts (liverworts do not have stomata). Our first set of completed experiments on Sphagnum capsules revealed that the principal role of the stomata here is to facilitate drying out rather than gaseous exchange. We are now analysing the function of stomata and the development of intercellular spaces in a range of key moss and hornwort taxa to provide experimental evidence to substantiate or negate the notion of their monophyly across land plants.
The phylogenetic distribution and functional significance of fungal endophytes in lower land plants. Cytological, experimental and molecular studies on fungal symbioses in liverworts are providing new insights into the origins of mycorrhizas in vascular plants. These investigations are not only revealing new kinds of symbioses but also indicate that liverwort –fungus symbioses almost certainly predated those in vascular plants.
I have ongoing interests in bryophyte ecology and conservation. I collaborate regularly with the UK statutory agencies and the British Bryological Society on the conservation of rare and endangered bryophytes (including in vitro cultivation and reintroduction trials).
Hooper E.J., Duckett J.G., Cuming A.C., Kumin W.E. and Pressel S. Ephemerella readeri C. Müell. (Physcomitrella readeri (C. Müell.) Stone & Scott, Funariidae, Musci, Bryophyta) a genus and species new to Europe. Journal of Bryology (under review)
Pressel S., P’ng K.Y.M., Duckett J.G. A cryo-scanning electron microscopy study of the water relations of the remarkable cell wall in the moss Rhacocarpus. Nova Hedwigia (in press)
Pressel S., P’ng K.Y.M., Duckett J.G. (2010). An ultrastructural study of the unique surface ornamentation in the liverwort Mizutania riccardioides Furuke et Iwatsuki. Bryologist (in press).
Pressel S. and Duckett J.G. (2010). Cytological insights into the desiccation biology of a model system: moss protonemata. New Phytologist 185, 944-963.
Duckett J.G., Pressel S., P’ng K.M.Y., Renzaglia K.S. (2010). The Sphagnum air-gun mechanism resurrected? Not with a closer look. New Phytologist (Letter) 185, 889-891. Corresponding author
Duckett J.G., Pressel S., P’ng K.M.Y. and Renzaglia K.S. (2009). Exploding a myth; the capsule dehiscence mechanism and the function of pseudostomata in Sphagnum. New Phytologist 183, 1053-1063. Corresponding author
Pressel S. (2009) Review of; Ochyra R., Lewis Smith R.I. and Bednarek-Ochyra H. 2008. The Illustrated Moss Flora of Antarctica. Cambridge, Cambridge University Press. Annals of Botany 104.
Pressel S., Duckett J.G., Ligrone R. and Proctor M.F.C. (2009). Effects of de- and rehydration in desiccation tolerant liverworts: a physiological and cytological study. International Journal of Plant Sciences 170, 182-199.
Pressel S. and Duckett J.G. (2009). Studies of protonemal morphogenesis in mosses. XII. Ephemeropsis, the zenith of morphological differentiation. Journal of Bryology 31, 67-75.
Duckett J.G. and Pressel S. (2009). London’s changing bryophyte flora. Field Bryology 98, 30-46. Corresponding author
Duckett J.G. and Pressel S. (2009). Extraordinary features of the reproductive biology of Marchantia at Thursley NNR. Field Bryology 97, 2-11. Corresponding author
Pressel S., Ligrone R. and Duckett J.G. (2008). The ascomycete Rhizoscyphus ericae elicits a range of host responses in the rhizoids of leafy liverworts; an experimental and cytological analysis. Fieldiana 47, 59-72.
Pressel S., Ligrone R. and Duckett J.G. (2008). The differentiation of moss protonemata; a cytological and experimental study. Annals of Botany 102, 227-245.
Pressel S., Ligrone R., Duckett J.G. and Davis E.C. (2008). A novel ascomycetous endophytic association in the rhizoids of the leafy liverwort family, Schistochilaceae (Jungermanniidae, Hepaticopsida). American Journal of Botany 95, 531-541.
Duckett J.G., Matcham H.W. and Pressel, S. (2008). Thursley Common NNR: bryophyte recolonization one year after the great fire of July 2006. Field Bryology 94, 3-11. Corresponding author
Pressel S., Matcham, H.W. and Duckett J.G. (2007). Studies of protonemal morphogenesis in mosses. XI. Bryum and allied genera: a plethora of propagules. Journal of Bryology 29, 241-258.
Rowntree J.K., Duckett J.G., Mortimer C.L., Ramsay M.M. and Pressel S. (2007). The formation of specialized propagules resistant to desiccation and cryopreservation in the threatened moss Ditrichum plumbicola Crundw. (Ditrichales, Bryopsida). Annals of Botany 100, 483-496.
Matcham H.W., Pressel S., Russell S., Massardo F. and Duckett J.G. (2007). Inventory and conservation of the bryoflora of south-western Patagonia. Field Bryology 93, 2-8.
Pressel S. and Duckett J.G. (2006). The parasitic ascomycete Mniaecia jungermanniae (Nees ex Fr.) Boud. induces the formation of giant perichaetia and apogamous sporophytes in leafy liverworts. Canadian Journal of Botany 84, 384-392.
Pressel S., Ligrone R. and Duckett J.G. (2006). Effects of de- and rehydration on food-conducting cells in the moss Polytrichum formosum Hedw.: a cytological study. Annals of Botany 98, 67-76.
Duckett J.G., Pressel S. and Ligrone R. (2006). Cornish bryophytes in the Atlantic Arc: cell biology, culturing, conservation and climate change. In: Botanical Links in the Atlantic Arc. (Eds SJ Leach, CN Page,Y Peytoureau and MN Sanford) English Nature and the Botanical Society of the British Isles, Conference Report 24, pp.165-177.
Pressel S., Duckett J.G. and Rowntree J. (2006). In vitro cultivation: its contributions to bryophyte ecology. Field Bryology 90, 48.
Rothero G.M., Duckett J.G. and Pressel S. (2006). Active conservation – augmenting the only British population of Bryum schleicheri var. latifolium via in vitro cultivation. Field Bryology 90, 12-16. Corresponding author
Pressel S. and Duckett J.G. (2005). Studies of protonemal morphogenesis in mosses. X. Ephemeraceae revisited; new dimensions underground. Journal of Bryology 27, 311-318.
Duckett J.G., Fletcher R., Matcham H.W., Read J.T., Russell A.J. and Pressel S. (2004). In vitro cultivation of bryophytes; practicalities, progress, problems and promise. Journal of Bryology 26, 3-20.
Pressel S. and Duckett J.G. (2004). In vitro culturing of rare bryophytes. Field Bryology 82, 34-37.
Duckett J.G. and Pressel S. (2003). Studies of protonemal morphogenesis in mosses IX. Discelium nudum: exquisite adaptation to unstable clay banks. Journal of Bryology 25, 241-246.