A Phylogenetic Evaluation of the Ramalina americana Chemotype Complex (Lichenized Ascomycota, Ramalinaceae) Based on rDNA ITS Sequence Data

The nature and significance of morphologically indistinguishable chemical races have been active areas of lichenological research for decades. This study uses a phylogenetic analysis of rDNA sequences to investigate whether the morphologically indistinguishable chemotypes of Ramalina americana are distinct species. Cladistic analysis of ITS sequences from 19 R. americana individuals (representing eight of the nine described chemotypes) and four outgroup Ramalina species reveals that R. americana comprises at least two cryptic, phylogenetic species. One, R. americana, is largely acid-deficient and occurs in the northern half of the range of the complex (and at high elevations in the Southern Appalachian Mountains); the other, R. culbersoniorum sp. nov., encompasses most of the chemical diversity and occurs in the southern half of the range. There is no meaningful resolution within either species. Among the outgroup Ramalina species, R. intermedia appears to be sister to the northern species, while R. fastigiata, the presumed sister group to the complex, forms an unresolved trichotomy with both the northern and southern species. Ramalina sinensis, often assumed to be closely related to the complex, is only distantly related. The results of this study agree with previous studies of other lichens in that each chemotype does not represent a separate species, nor are they all conspecific. Rather, the complex can be divided into two species, each consisting of multiple chemical races. Secondary-product chemistry has been an important tool in lichen systematics for over a century (Elix 1996; Hawksworth 1976). Since Nylander's (1866) first applications of thallus spot-tests to lichens, it has been recognized that many morphologically similar species of lichens can often be separated on the basis of their secondary products. Many morphs, however, comprise multiple, visually indistinguishable chemical races (chemotypes). In some organisms, such as pines (Yazdani et al. 1985), it is often easy and accurate to recognize such chemical variants as within-species polymorphisms because the secondary products vary only in their proportions to one another, and this variation is gradual across a given morphological species' geographical range. In lichens, however, chemical variation is often discrete: different chemotypes usually have qualitatively different compounds and largely non-overlapping geographic ranges. In cases where certain lichen chemotypes share some or all of the same compounds (chemosyndromic variation-Culberson & Culberson 1976; Feige & Lumbsch 1995), the relative proportions of these compounds usually vary in a discrete and predictable fashion. In addition, a strong genetic component to lichen chemistry has been demonstrated (C. E Culberson et al. 1983, 1988), and over the years, workers have correlated chemotype with ecology, geography and/or micromorphology (W. L. Culberson 1986) in various lichens. Given this evidence, the elevation of many lichen chemotypes to species status is justifiable; however, it is often a point of contention. Arguments for (W. L. Culberson 1969, 1986; Poelt 1972) and against (Almborn 1965; Lamb 1951; Rogers 1989) recognizing lichen chemotypes as species have been presented and the debate is ongoing (Lumbsch 1998a). Recently, the investigation of chemosyndromic variation within previously poorly known taxa has been advocated (Zeybek et al. 1993). The careful correlation of chemosyndromic variation with other types of character variation (a posteriori evaluation of chemical characters; Lumbsch 1998a, b) has shown that the presence of a biogenetic series of chemosyndromes can be more important for species recognition than the presence or absence of individual compounds. The present study addresses the phylogenetic utility of chemistry in the Ramalina americana chemotype complex. Ramalina americana is a group of small, tufted lichens that reproduce exclusively by spores. These lichens grow on hardwood trees throughout the eastern United States and Canada (Fig. 1). The species was separated from the European R. fastigiata by Hale (1978), who described a northern, acid-deficient race (R. americana sensu stricto) and a southeastern population consisting of multiple chemotypes. Dey (1978) de0007-2745/99/602-618$1.85/0 This content downloaded from 207.46.13.131 on Sun, 16 Oct 2016 05:14:28 UTC All use subject to http://about.jstor.org/terms 1999] LAGRECA: RAMALINA AMERICANA 603