Genus Retama in Subfamily Papilionoideae
In botanical taxonomy, a genus (plural genera) is a rank used to group closely related species within a family. In the hierarchy, genus sits below family and above species.
Genera are defined by shared morphological, anatomical, and genetic characteristics (for example, features of flowers, fruits, seeds, or leaves) that indicate a close evolutionary relationship among the species they contain.
Each genus can include one or more species. Examples include Rosa (roses) and Solanum (nightshades, including tomato and eggplant).
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Genus Description
Suggest a correction!Family Fabaceae (Leguminosae), subfamily Faboideae, tribe Genisteae. The genus comprises approximately five species of broom‑like shrubs distributed across the Mediterranean basin, from the Iberian Peninsula and North Africa eastwards to the Levant. The type species is Retama monosperma (L.) Boiss., originally described as Spartium monospermum (POWO, 2024; WFO, 2024; Lewis et al., 2005).
Shrubs or small trees, often with a broom‑like habit of slender, upright, virtually leafless shoots. Leaves are reduced to minute scales; when present they are simple or trifoliate, with linear leaflets; stipules are absent. Inflorescences are terminal or axillary racemes or short panicles. Flowers are papilionaceous, with a broadly reflexed standard, two wing petals, and a keel formed by two fused petals; the calyx is tubular–campanulate, five‑toothed. The ovary is sessile with 2–6 ovules; the fruit is a flat, dehiscent legume pod containing one to several seeds (Lewis et al., 2005; Díaz et al., 2015).
Four of the five taxa are concentrated in the western Mediterranean: R. monosperma and R. sphaerocarpa occur from Spain and Portugal to Morocco and Algeria, while R. raetam extends to the eastern Mediterranean. A single island endemic, R. canariensis (syn. Genista canariensis), is restricted to the Canary Islands. Species occupy dry, open habitats—scrub, maquis, phrygana and coastal dunes—usually below 800 m elevation (POWO, 2024; WFO, 2024).
The genus is entomophilous; flowers attract bees and lepidopterans with typical nectar guides. Pods dehisce explosively, dispersing seeds a short distance; many seeds have a hard seed coat aiding dormancy. Chromosome counts are consistently 2n = 48, a figure that aligns with the tribe‑wide base number x = 8 (Miller & Nyberg, 1998).
Molecular phylogenies place Retama within the core Genisteae, sister to the clade comprising Genista and Cytisus (Lewis et al., 2005; Díaz et al., 2015). While some floras treat Retama as a subgenus of Genista, recent phylogenetic evidence supports its generic status, albeit with taxonomic flux for the placement of R. raetam, which some authors retain in Genista (WFO, 2024).
Several species are cultivated as drought‑tolerant ornamentals and for dune stabilization; R. monosperma is used in Mediterranean landscaping and reclamation projects. The genus is not a major food or timber source, and it contains no medicinal taxa of commercial importance.
Most populations are widespread, but island endemics such as R. canariensis face habitat loss and invasive competition; further monitoring and ex situ conservation are advisable.
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Retama dasycarpa (Coss.)
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Retama monosperma ((L.) Boiss.)
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Retama raetam ((Forssk.) Webb)
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Retama rhodorhizoides ((Webb & Berthel.) Webb & Berthel.)
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Retama sphaerocarpa ((L.) Boiss.)