Common name: Florida rosemary.
Distribution: All of Florida west to Mississippi, north to South Carolina. Listed as treatened in Georgia.
Habitats: Florida rosemary grows on excessively to well-drained sandy soils in Florida scrub. Florida rosemary is a local structural dominant on mature coastal dunes, also can dominate white sand knolls in scrub on the Lake Wales Ridge and other ancient inland dunes of Florida (Austin et al. 1987). It can occur intermixed with scrub oaks on white sand and is occasional in dry scrub on yellow sand, especially in previously disturbed areas. Florida rosemary occurs on coastal dunes in Mississippi, and river dunes and sand ridges of Georgia and South Carolina (Godfrey 1988).
Description and Life History: This species is a much-branched perennial evergreen shrub, growing over 1.5 meter in height.”. Large plants are often growing in spherical mound that may be comprised of several indistinguishable individuals. Seedlings have distinctive, symmetrical patterns of leaf insertion in 4’s or 6’s. The leaves are strongly revolute (needle-like) leaves 8-12 mm, opposite to whorled. Florida rosemary has tiny flowers, bronze or yellowish in color, and clustered in leaf axils. The fruit is a two-seeded yellow-green drupe to 3 mm diameter (Godfrey 1988). Only 20% of biomass is held belowground, and the plants are shallowly rooted (Johnson et al. 1986). Rosemary plants are killed by fire. Fire return intervals for inland populations are highly variable at 15-100 (Menges 2007) but frequent of fires (<20 years) results in significant loss (>35%) of rosemary scrub habitat (Gehring et al. unpublished data). Post-fire recovery occurs with germination of seeds from the soil seedbank. Seedlings generally appear aboveground beginning the second winter after burning and little seedling recruitment occurs after about five years post-fire.
Phenology: Seedlings may be found throughout the year. Florida rosemary flowers in the fall through spring and summer, with fruits most typical late in the year.
Breeding System and Pollination: Florida rosemary is dioecious (separate male and female plants, usually in approximately equal numbers). The flowers are pollinated by wind.
Genetics: Ceratiola s a monotypic genus. Limited genetic research has been conducted using isozymes; 64.7% of 17 loci polymorphic, with 2.55 alleles per polymorphic locus with mean gene diversity of 0.141 (McDonald and Hamrick 1996). One study found different patterns in spatial genetic structure in two populations possibly related to fire return interval and intensity (Trapnell et al. 2008). Although common in southeastern states, rosemary populations in central Florida are the center of genetic diversity while populations in other states represent subsets of these populations (Trapnell et al. 2007).
Population Dynamics: All plants that are burned will die, but patchy fires that are typical in many habitats may leave patches of surviving plants. Salt-spray and storms can induce mortality in coastal habitats. Seeds remain viable in the soil seed bank for up to 8 years and require scarification (by sand movement, animals or disturbance) to germinate. Seedlings recruit for 2-5 years following disturbance and annual survival exceeds 98%. Thinning due to resource competition occurs between 10 to 20 years. Seedling grow 4-7 cm per year and add 0.6 nodes annually, less than previously thought, making node counts an underestimate of true age. Plants reach reproductive age as young as 4 with males typically flowering before females. Flowering peaks between 20 and 30 years. Sex ratios are approximately 1:1 with a slight bias towards females. A study in Coastal Plain sandhills found a similar ratio except for a bias towards females in long unburned habitats (Schmidt 2008). Plants may lose productivity and begin partial dieback after 20 years, but some plants can survive in excess of 50 years. Although 50 year old individuals have been found, after age 35 large branches may rest on the ground and successfully root as the rest of the plant dies back (Johnson 1982). Inland stands are typically dominated by a single cohort or a few cohorts, whereas coastal populations are all-aged.
Interesting Facts: Florida rosemary is allelopathic, particularly to herbaceous plants endemic to inland ridge systems (Hunter and Menges 2002; Hewitt and Menges 2008) although allelopathy does not affect all species (i.e. Liatris ohlingerae; Weekley et al. 2008).. The chemical responsible for inhibiting germination, ceratiolin, has been isolated (Tak et al. 1993). The slow recovery after fire provides microsites for colonization of these herbs, including many that are endemic and/or endangered (Richardson and Williamson 1988; Menges and Kohfeldt 1995). Herb populations continue to find refuge in the persistent gaps among rosemary shrubs until these sandy microsites are altered by colonizing lichen and litter accumulation. Drupes are consumed by birds, which can disperse the viable seeds. Harvester ants and mice eat seeds (Johnson 1982). Florida rosemary provides nesting sites for northern cardinal, grey catbird, yellow-rumped warbler, Florida scrub-jay treatened), common yellowthroat, and mourning dove (Woolfenden 1973). In hotter parts of the year, dense stands exude a distinctive honey-like odor.
Rosemary plants and its associated scrub habitat has been found to host a variety of rare insect species. A rare plant bug Keltonia balli (Knight) was discovered on only the male flowers of rosemary plants at both nymph and adult life stages (Wheeler 2009). The grasshopper species Schistocerca Ceratiola feeds exclusively on the leaves of rosemary (Capinera et al. 2001). The openness of this habitat makes rosemary scrub the preferred habitat for a burrowing wolf spider, Geolycosa xera archboldi (Carrel 2003).
Data Collected by Archbold Biological Station’s Plant Ecology Lab: We collect long term demographic data on postfire cohorts: annual recruitment, growth, mortality, density and age structure postfire. We are currently studying six populations. We also have collected data on size, gender, and spatial distribution of rosemary shrubs at two sites (Gibson and Menges 1994). We are further examining spatial dynamics of Florida rosemary recruitment post-fire mapping recruitment locations, densities, growth, and survival in relation to other rosemary seedlings.
Data Availability: No data are available at the present time.
Contact Person: Eric S. Menges