Morphological Analyses of theMecardonia acuminata(Plantaginaceae) Species Complex in the Southeastern USA

The Mecardonia acuminata complex is a classic example of a widespread endemic species in the southeastern US. Morphological variations in the complex resulted in the classification of at least three varieties or subspecies for the species by previous botanists. However, the distributions and diagnostic features of two of the subspecies, peninsularis and microphylla, are unclear due to shared morphological features and widespread distribution of the subspecies acuminata. The present study involved examination and biostatistical analyses of 3 vegetative and 5 reproductive characters that were known to serve as diagnostic features of 1 or more taxa of the species. Results of the study indicate that subspecies peninsularis can be distinguished by its ascending peduncle angle of suspension, diffuse basal branching habit (dendriform at base) of the shoot and small leaves, especially in the southern ranges of the complex. Subspecies microphylla can be distinguished based on its short (<20 mm) fruit peduncles and divaricate peduncle angle of suspension. Subspecies acuminata comprises individuals with divaricate peduncle angle of suspension and long fruit peduncles (>20 mm). Subspecies acuminata was also observed to comprise many individuals that were intermediates of 2 or 3 subspecies. Discriminant function analyses on longitude, latitude, and biogeography as well as Wilks' lambda estimates suggest moderate to low clinal variation and a much broader historical range distribution of subspecies peninuslaris. The morphological variations in the species complex may be due to secondary contact with ongoing integration into subspecies acuminata.