defining relict plant species

[Ms Anolia Lynch]

The concept of a relic(t) plant species has been used as an important character of a species in conservation assessments in Australia.  This concept relates to the conservation of species and environments that were more common in the past and that are indicative of evolutionary processes.  Relict species are defined in Lincoln et al. (1998, p. 260) as:  “1. Persistent remnants of formerly widespread fauna or flora existing in certain isolated areas or habitats;  relic.  2. A phylogenetic relict;  the existence of an archaic form in an otherwise extinct taxon.”  

While phylogenetic relicts are relatively easy to identify, it is more difficult to define which taxa now occur in remnant distributions.  Even the related concept of distinguishing between neo-, holo- and palaeoendemics is rarely attempted.  

However, categorisations of relict plants were made in the 1970s based on the retention of (a) floral characters generally accepted by taxonomists and morphologists as primitive, and (b) early stages in the evolution of the leaf, shoot and inflorescence morphologies.  There are some 592 relict seed plant species retaining primitive floral characteristics listed for Australia by Specht et al. (1974), and 381 species of angiosperms retaining primitive morphological characters.

Australian examples given in Melville (1973) of (a) include Eupomatia laurina and E. bennettii (Eupomatiaceae), Himatandra (Himatandraceae), Austrobaileya (Austrobaileyaceae) and Blepharocarya (Anacardiaceae).  Examples of (b) include Stirlingia spp. (Proteaceae);  to the extent that Melville related characters of S. tenuifolia, S. simplex, S. abrotanoides and S. teretifolia to branch systems found among plants of the Psilophytales of Silurian to Devonian age, and S. latifolia leaf characters to fossil leaves of Gangamopteris of Permo-carboniferous age.  However, the relationship of characters of Palaeozoic plants to angiosperm lineages that did not begin to evolve until the Cretaceous, and species extant in the Holocene (some 200 million years later) must be tenuous.  The concept is more tenable in terms of groups such as the Cycads and conifers that are presumed to be much older, however, can these lineages still be used to infer that extant descendants are primitive?

I would welcome any comments in regard to relict species (and refugia), and related (preferably more recent) literature, as the relationships between species and their degree of environmental adaptation is of particular interest to me.

Jasmyn Lynch
PhD student
University of Queensland
Email:  s4023888 at student.uq.edu.au