Bigelowia nuttallii

Although clearly distinct, this species may be confused with its congenor B. nudata (Michx.) DC. At a glance, it can even be easily mistaken for the very common Euthamia minor. In Euthamia the heads have ray flowers (the corolla appears to be composed of only one large petal) and in Bigelowia the flowers are all discoid (rotate, actinomorphic). The clearest difference between B. nuttallii and B. nudata is in the habit. B.nuttallii is rhizomatous and becomes colonial or loosely matted while B. nudata occurs in small clumps or singly. Although Anderson (1970, 1972) cites several other characters that separate the two, examination of specimens at FLAS gave this researcher the impression that the phenotypic variability is high in both Bigelowias found in Florida and that the habit character is the only easily observable one that is consistent. This is especially true when comparing the Pinellas Co. specimens of B. nuttallii to B. nudata subsp. australis L.C. Anderson which Anderson (1970) says has a morphology that is intermediate between B. nudata subsp. nudata and B. nuttallii in many respects. The Pinellas Co. population exhibits gigantism that results from polyploidy in that location (Anderson, pers. comm. 1993).

The general habitat preference of this species is fairly restricted. It normally occurs on sandstone or siltstone outcrops from Georgia to eastern Texas. These are often Eocene to Pliocene strata. Substrates include the Altamaha Formation (Altamaha Grit, Miocene Epoch) in GA, Lithonia Gneiss (granite rock outcrops) in Rockdale and Walton Cos., GA, carboniferous period sediments (Pennsylvanian sandstone outcrops) in AL and (Anderson 1970, Patrick, pers. comm. 1992). The location of populations on only some granite outcrops, and not on Pennsylvanian sandstone in GA is not understood. In the Altamaha Formation the plant is frequent, often on tiny outcrops where rarer grit endemics have not yet been located. The species is an aspect dominant in the fall on numerous outcrops in Georgia's inner coastal plain. These habitats also harbor Selaginella acanthanota complex Arenaria uniflora and Talinum mengiesii (Patrick, pers. comm. 1992). These plants appear not to be fire-dependent, but adapted to thin soils.

The Florida population at The Nature Conservancy's Rock Hill Preserve is on an Altamaha Grit outcrop (Harper 1911). However, the species has also been found in Pinellas Co. in sand pine scrub (Anderson 1970) and among disturbed mixtures of sand pine and slash pine (See Garrett s.n. FLAS, Wunderlin #10362 FLAS). At the Rock Hill Preserve and elsewhere in its range B. nuttallii occurs on very thin soils immediately over non-calcerous rock (Gholson 1992, pers. comm.; Harper 1911). The soils are generally low (0.5-2.5%) in organic matter and cation exchange capacity (Anderson 1972). Harper (1911) reports that B. nuttallii is second only to Aristida stricta in abundance on the Rock Hill site.

Habitats for this species seem to be open, perhaps periodically disturbed sites. Other species within common habitats respond to fire with increased growth and flowering and may be adapted to this type of natural disturbance (Angus Gholson, pers. comm. 1992). Anderson (pers. comm. 1993) suggests that very hot fires may impact rhizomes and roots, which are constrained to shallow soil pockets and rock crevices.

Due to its rhizomatous nature B. nuttallii forms loosely interwoven mats and can spread vegetatively as well as by seed. It blooms in September and October, producing seed shortly afterwards. Chromosome numbers of n=9, 18 and 27 have been recorded for the species with all three ploidy levels occurring in Florida, the diploids being at Rock Hill and both tetraploids and hexaploids occurring in Pinellas Co. (Anderson 1977). Specimens examined at FLAS showed fully differentiated styles as well as well formed and apparently functional pollen.

Bigelowia nuttallii may hybridize with B. nudata in a few populations in GA, where morphologically intermediate plants were observed (Anderson, pers. comm. 1993). Diploids of both species are basically outcrossers although B. nuttallii is much more successful in terms of autogamous seed production than B. nudata (Anderson 1977). The reproductive system in the polyploids has not been investigated.