FABACEAE

Weakley, Alan S., Poindexter, Derick B., Medford, Hannah C., Franck, Alan R., Bradley, Keith A., Sadle, Jimi & Kelley, John Michael, 2021, Studies In The Vascular Flora Of The Southeastern United States. Vii, Journal of the Botanical Research Institute of Texas 15 (1), pp. 23-56 : 44

FABACEAE

Chamaecrista : Chamaecrista horizontalis , a new species of the Southeastern Plains ecoregion, is distinct from C. deeringiana , a species endemic to the southern Florida pine rocklands .

Primary author:Alan R. Franck

Chamaecrista fasciculata (Michx.) Greene is a tap-rooted, usually monocarpic species that is widespread in the eastern United States. It is typically treated as a polymorphic species ( Irwin & Barneby 1982) or comprising a few varieties (Isely 1975, 1998; Weakley 2020), but historically had been separated into eight species in North America ( Britton & Rose 1930; Small 1933). Perennial plants with the main root(s) horizontal (Pullen 1963; Fig. 13 ), which otherwise appear superficially identical to C. fasciculata , have been referred to as C. deeringiana Small & Pennell. Chamaecrista deeringiana was first considered endemic to extreme southern Florida ( Pennell 1917; Britton & Rose 1930; Small 1933) in the Southern Florida Coastal Plain ecoregion, and the name was later applied to plants in the southwestern part of the Southeastern Plains ecoregion (EPA 2003) of Alabama, Florida, Georgia, and Mississippi ( Cronquist 1949; Pullen 1963; Irwin & Barneby 1982; Sorrie & Leonard 1999).

Closer scrutiny reveals that C. deeringiana should be reverted to its original concept as endemic to extreme southern Florida, and that perennial plants in the Southeastern Plains ecoregion are morphologically distinct, here described as a new species, C. horizontalis . Root length, anther color, and habitat distinguish the two perennial species, which are separated by ca. 700 km. Chamaecrista deeringiana has been frequently misapplied to plants in peninsular Florida north of Miami and the Keys, but none are known to be perennial with the primary root horizontal. In the literature, the subterranean, horizontal parts of these perennial species have been described as roots or rhizomes, but from anatomical studies of transverse sections, Pullen (1963) concluded they were roots, not rhizomes.

Notably, the recognition of two species formerly lumped into C. deeringiana makes each an endemic species fitting sensibly into the typical endemism patterns in the southeastern United States Coastal Plain ( Sorrie and Weakley 2001). Chamaecrista horizontalis is an East Gulf Coastal Plain endemic (Pattern #10), a pattern shared by more than 80 vascular plant taxa, and C. deeringiana (in its narrowed circumscription) is an exemplar of Subtropical Florida endemism (Pattern #9), which has over 50 endemic vascular plant taxa ( Sorrie & Weakley 2001). Each species is now recognized as a narrow endemic ( C. deeringiana ) or moderately narrow endemic ( C. horizontalis ), and each warrants a conservation rank of G3 (= Vulnerable) ( NatureServe 2020).

Based on field work and herbarium studies, Pullen (1963) concluded that the perennial species (here as C. deeringiana and C. horizontalis ) do not hybridize with C. fasciculata . The perennial species are relatively short plants (to 60 cm tall) and usually have several stems arising from the horizontal root ( Fig. 13 ). Pullen (1963: 32) found that the growth form of the perennial species was maintained between field and greenhouse plants, while branching habits and height among the eight varieties of C. fasciculata recognized by him noticeably varied. Crossing experiments with greenhouse plants of various taxa were inconclusive and no F1 progeny were raised from the very few fruits that did develop (Pullen 1963).

Figures

FIG. 13.A,C.Chamaecrista deeringiana, Goulds,Miami-Dade Co.(photos by A.R. Franck).B. Chamaecrista horizontalis, isotype (NY);image courtesy of the C.V.Starr Virtual Herbarium of the New York Botanical Garden,http://sweetgum.nybg.org/science/vh/.D.Chamaecrista horizontalis, Davis 16081 (FLAS,sheet 2 of 2); image by Sophie Charles,courtesy of the University of Florida Herbarium (FLAS),Florida Museum of Natural History.