Lupinus westianus

Lupinus westianus, commonly known as the Gulf Coast lupine, is a species of flowering plant in the family Fabaceae. It is endemic to the Florida Panhandle in the southeastern United States.

Description

Lupinus westianus is a perennial, suffrutescent herb characterized by erect growth and a woody base. Plants typically reach 60–85 cm in height.

Leaves are unifoliolate, elliptic to ovate, usually 7.5–9.0 cm long and 3.5–4.5 cm wide, with appressed pubescence covering both stems and leaf surfaces.

The flowers are blue, ranging from light to dark shades, and possess a distinctive maroon to purplish-blue central eyespot on the banner petal.

Taxonomy

The species was first described by John Kunkel Small in 1926.

Two subspecies are recognized:

• Lupinus westianus ssp. westianus – the typical form, occurring across much of the Florida Panhandle
• Lupinus westianus ssp. peninsularis – restricted to peninsular Florida

Lupinus westianus belongs to a group of unifoliolate, evergreen lupines native to the southeastern United States, many of which are geographically restricted and associated with sandy, fire-maintained habitats.

Comparison with related species

Lupinus westianus is a member of the unifoliolate Lupinus complex of peninsular Florida, a group of closely related taxa segregated from the historically broad concept of Lupinus diffusus based on morphological and geographic differentiation.

Within this complex, species are distinguished primarily by leaf pubescence (density and whether the green surface is visible), leaf proportions, floral characters (especially the banner eyespot), growth habit, and geographic distribution.

Lupinus westianus is distinguished by its generally more robust habit, broader leaves, and restriction to southern Florida and the Florida Keys. It is further divided into two subspecies, reflecting geographic and morphological variation within the species.

It differs from related species as follows:

• Lupinus floridanus — typically less robust, with narrower, more elongate leaves and only moderate pubescence that does not obscure the green leaf surface; distributed primarily in central and northern peninsular Florida.

• Lupinus cumulicola — leaves densely silky-pubescent, giving a silvery appearance that obscures the green surface; generally smaller and associated with central Florida ridge and scrub habitats.

• Lupinus pilosior — similar to L. cumulicola in having dense pubescence but typically more compact and with even more persistent hair coverage; not characterized by the broader leaves and robust habit of L. westianus.

• Lupinus ocalensis — differs in leaf morphology, pubescence, and floral traits and is geographically restricted to central Florida ridge systems, particularly the Ocala region.

• Lupinus diffusus (sensu stricto) — more widespread outside peninsular Florida and differing in leaf and floral characteristics; many Florida populations formerly assigned to this species are now segregated into distinct taxa including L. westianus.

• Lupinus villosus — a more widespread southeastern species with densely silky, silvery foliage but typically differing in overall morphology and occurring primarily in longleaf pine sandhills and disturbed sandy habitats outside the southern Florida range of L. westianus.

These distinctions reflect a radiation of closely related taxa adapted to xeric, fire-maintained sandy habitats of peninsular Florida, with Lupinus westianus representing a southern lineage characterized by its larger size and broader leaves.

Distribution and habitat

Lupinus westianus is endemic to the Florida Panhandle, where it occurs in coastal dunes and longleaf pine sandhill ecosystems.

It typically inhabits sandy, well-drained soils in open, fire-maintained environments. These habitats are characterized by high light availability and periodic disturbance, which are important for maintaining suitable conditions for the species.

Phenology

Flowering occurs from March to May.

Genetics and phylogeny

The complete chloroplast genome of Lupinus westianus has been sequenced, revealing a genome approximately 154,270 base pairs in length.

The genome contains 130 genes, including protein-coding, tRNA, and rRNA genes, with several duplicated in inverted repeat regions.

Phylogenetic analyses place L. westianus firmly within the genus Lupinus, with close relationships to species such as Lupinus luteus and Lupinus albus.

Genetic evidence suggests that populations may have reduced genetic diversity due to habitat fragmentation, which may have implications for long-term conservation.

Conservation

Lupinus westianus is considered globally imperiled (G2) by NatureServe due to its restricted range and specialized habitat requirements.

Threats include habitat loss from development, alteration of natural fire regimes, and fragmentation of longleaf pine ecosystems. Conservation efforts focus on habitat protection and the maintenance of prescribed fire regimes.

References