Warea carteri Small (Brassicaceae)
Common Name: Carter’s mustard

Distribution: On the Lake Wales Ridge in Lake, Polk, and Highlands counties, Florida; historically, also known from Atlantic Coastal scrub.

Habitats: Carter’s mustard occurs primarily on yellow sands, in oak-hickory scrub and  sandhill, and on gray sands in scrubby flatwoods.

Description: Carter’s mustard is a single stemmed, many-branched herb to 1 m in height.  Small white four-petaled flowers occur in globular inflorescences the size of ping-pong balls. The flowers are perfect, with six stamens and a superior ovary. The fruit is a silique, a legume-like pod that dehisces at maturity to release tiny gravity-dispersed seeds.

Life History: Carter’s mustard is an annual. Plants of a given cohort reach sexual maturity in the early fall (Sept-Oct) and produce seeds which are shed over the next two to three months. Seedling recruitment occurs from July to March (i.e., recruitment begins prior to fruiting of the previous year’s cohort), so that there is an overlap of cohorts.

Phenology: Seedlings often remain as rosettes throughout the dry fall-spring season.  Seedling mortality is generally highest late in the dry season (Apr-May). Plants that survive the spring drought typically bolt, often doubling in height from month to month.  However, there appears to be considerable temporal and spatial variation in growth rates, perhaps having to do with differences in annual rainfall or in microhabitat. For example, seedlings recruiting in shadier microsites seem to elongate sooner than those in sunnier microsites.

Breeding System and Pollination: Carter’s mustard is self-compatible and spontaneous self-fertilization (autogamy) frequently occurs. Fruit set from autogamous crosses is lower than experimental hand-pollinated self- and outcrosses, and seed set is lower than both hand pollinations and open pollinated controls. Floral morphology indicates a generalist insect pollination syndrome. Flowers are visited by insects of several orders, including bees, flies and wasps. Nonetheless, Carter’s mustard is pollinator-limited since hand pollinations result in greater fruit and seed set than open pollinated controls. 

Genetics: Genetic diversity is lower in Carter’s mustard than in other species with similar ecological and life history traits. A relatively large proportion of the detected diversity (30.4%) occurs among rather than within populations. Genetic diversity is spatially organized, with a significant north-south cline in allele frequencies at one locus.

Population Dynamics: Carter’s mustard is a fire-respondent annual. Aboveground populations experience dramatic booms in the first year following fire, followed by equally dramatic crashes in the second postfire year. Small fluctuating populations may persist in mechanically disturbed sites like firelanes or trails. The sudden (re)appearance of large aboveground populations following fire suggests the presence of a long-lived seedbank. Current research is investigating seedling demography and seedbank dynamics.

Interesting Facts: Historical records indicate that Carter’s mustard was once significantly more widespread than it is today, occurring in Brevard, Miami-Dade, and Glades counties. These populations apparently have all been extirpated.  Florida Natural Areas Inventory lists records from Lake County from the early ‘90s, but recent searches have failed to relocate these.

Data Collected by Archbold Biological Station’s Plant Ecology Lab: The Plant Ecology Lab has investigated the breeding system and genetics of Carter’s mustard.  Annual surveys of scores of sites have been conducted at The Nature Consevancy’s Tiger Creek Preserve, Archbold Biological Station, and Lake Placid Scrub since 1988 and at Lake Wales Ridge State Forest since 1995. Monthly seedling survival surveys have been conducted monthly at the State Forest since 1996 and at ABS since 1999.  Numerous lab and field germination experiments have also been conducted over the last several years.

 Data Availability: Data from annual surveys at Tiger Creek Preserve and Lake Wales Ridge State Forest are available on this Web site.

Contact Person: Carl W. Weekley

References:

1. Evans, M.E.K., R.W. Dolan, E.S. Menges, and D.R. Dolan. 2000. Genetic diversity and reproductive biology in Warea carteri (Brassicaceae), a narrowly endemic Florida scrub annual. American Journal of Botany 87:372-381.
2. Menges, E. S., and D. R. Gordon. 1996. Three levels of monitoring intensity for rare plant species. Natural Areas Journal 16:227-237.
3. Menges, E.S., R.W. Dolan, R. Yahr, and D.R. Gordon. 2001. Comparative genetics of seven plants endemic to Florida’s Lake Wales Ridge. Castanea  66:98-114.
4. U.S. Fish and Wildlife Service. 1999. Carter’s mustard. Pages 1972-1978 in South Florida multi-species recovery plan. U.S. Fish and Wildlife Service, Atlanta, Georgia, USA.

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