Title : Flow cytometry as a support tool for the identification of semi-cryptic species
Abstract:
While floristics is the science that tries to elaborate tools for identifying plant biodiversity, taxonomy is the science that tries to distinguish biological entities, mainly genera, species, and infraspecific taxa (subspecies, etc.). Unfortunately a significant proportion of species or subspecies are not obvious to distinguish to the eye. Closely related species which do not bear evident macro-/micro-morphological criteria to discriminate them are classically termed ‘cryptic species’, and we used here ‘semi-cryptic’ when they only just bear a few subtle criteria. These semi-cryptic species are also very controversial within the scientific community because some (called lumpers) consider subtle characters only as part of the variability of the species and others (called splitters) consider them sufficient to circumscribe distinct species. A large part of these cryptic or semi-cryptic species or subspecies belongs to polyploid complexes, including hybridisation by allopolyploidy. Indeed, polyploidy is not only a major and rapid cause of speciation in vascular plants, it is also a major problem for the interpretation of phylogenies and their use in the delimitation of species. Thus, in polyploid complexes DNA phylogenies are hardly helpful and knowing the ploidy level of plants would be auspicious to help taxonomists identify semi-cryptic species and/or confirm the reliability of various prospective morphological criteria. Therein, even if it is not as accurate as chromosomal counting, flow cytometry is a relative cheap and rapid method to quantify the DNA content and consequently to estimate the ploidy level of a plant individual or organ. We have measured DNA content of hundreds of plant individuals and populations of several species and subspecies of various genera where polyploidy complexes are known, mainly Monocots as Amaryllidaceae (Allium, Narcissus), Asparagaceae (Muscari, Prospero, Oncostema) and Poaceae (Avena, Avenula, Brachypodium) but also Dicots as Araliaceae (Hedera) or Ferns as Aspleniaceae (Asplenium). In species-poor but overlooked complexes as Avena, Brachypodium or Muscari, we were able to confirm the presence of semi-cryptic species as new records for continental France. In another similar case as Asplenium and Oncostema we just initiated a reference database in order to explore cryptic biodiversity in understudied areas as Algeria. In the ivies (Hedera), introduced ornamental material is frequent in urban areas and cytometry helped us to confirm identification and consequently the probable geographical origin of the introduction. Finally, in species-rich and/or highly polyploidy complexes as Allium, Avenula, Narcissus or Prospero, ploidy levels help us to understand species delimitation and to achieve reliable criteria for clarifying synonymy and/or describing new taxa (classical species or natural hybrids).
