Abstract Detail

The evolution and ecology of aquatic bryophytes

Mishler, Brent [1], Shevock, James [2].

The evolution and ecology of rheophytic mosses.

"Rheophyte" is a term referring to a special type of aquatic plant: a plant that grows submerged for part of the year, but that is emergent at other times.  Such plants endure an unusual range of mechanical and physiological stresses that threaten their survival and reproduction.  A number of phylogenetically separate lineages of mosses have become rheophytes.  They are generally julaceous with lanceolate leaves, and many have multistratose leaf borders or thickened costae (=leaf midrib).  Most are dioicous, and sporophytes remain unknown or are exceedingly rare for many.  They are able to tolerate white water rapids with the sandblasting effect of sediments, and are able to deal with prolonged periods of desiccation, surviving in full sun during the dry season.  Adjacent rivers can have a considerably different species composition of rheophytes.  To establish new populations, rheophytes have to disperse over large areas of non-suitable habitat (generally forested), and then manage to get a foothold in this challenging environment.  For dioicous species to produce sporophytes, colonization has to occur independently at least twice.  The timing of gametangial production, fertilization, and sporophyte development must be greatly affected by the seasonality of water levels, yet few studies on reproductive biology of rheophytes have been done.  Only about 250-300 species of bryophytes worldwide are rheophytic.  Some whole families are basically rheophytic such as Cinclidotaceae, Fontinalaceae, and Scouleriaceae, but in general rheophytes are scattered phylogenetically within families that are mostly terrestrial. Many rheophytes represent long phylogenetic branches, without close living relatives, with a number treated as monospecific genera. That fact, coupled with the observation that most rheophytes have extremely restricted ranges, leads to a hypothesis that rheophytism is correlated with paleoendemism.  This hypothesis needs to be tested using phylogenetic comparative methods.  If the correlation holds, an explanation will be needed for how such a seemingly harsh environment could enhance the resistance of rheophytes to extinction.

1 - University Of California, Berkeley, DEPT OF INTEGRATIVE BIOLOGY, 1001 Valley Life Science Building # 2465, Berkeley, CA, 94720-2465, USA, (510) 642-6810
2 - California Academy of Sciences, Dept. Of Botany, 55 Music Concourse Dr., Golden Gate Park, San Francisco, CA, 94118, USA

Keywords:
Mosses
aquatic plants
rheophyte
Paleoendemism.

Presentation Type: Symposium or Colloquium Presentation
Session: SY02
Location: Payette/Boise Centre
Date: Monday, July 28th, 2014
Time: 2:45 PM
Number: SY02004
Abstract ID:868
Candidate for Awards:None