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Genus Roldana in Tribe Senecioneae

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

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Roldana (La Llave) is a genus of Asteraceae, tribe Senecioneae (APG IV, 2016). It contains roughly 45 species (POWO, 2024) distributed primarily in the highlands of Mexico, extending into Central America and the southwestern United States. Its members occupy pine‑oak forests, cloud forests and sub‑alpine grasslands at 1500–3200 m. The type species designated by La Llave is Roldana glabrata (Nesom, 1994).

Plants are herbaceous perennials or subshrubs bearing opposite to alternate, simple, glandular‑pubescent leaves. Terminal panicles or corymbs of radiate or discoid heads have cylindrical involucres with 2–3 phyllary series. Yellow florets have five fused anthers, a bilobed style, and the inferior ovary produces a compressed achene crowned by a long silky pappus for wind dispersal. These characters distinguish Roldana from most Mexican Senecioneae (Nesom, 1994).

Species richness peaks in the Sierra Madre Occidental and the Trans‑Mexican Volcanic Belt, where many taxa are narrow endemics (e.g., Roldana oaxacana and Roldana humboldtiana). Typical habitats include pine‑oak woodlands, cloud forests and montane grasslands; a few species occur on limestone outcrops or volcanic scree. Geographic isolation mirrors historical splits of the Mexican highlands (Sklenar et al., 2019).

Flowers attract generalist pollinators such as native bees and Lepidoptera; field observations of Roldana affinis recorded Colias visits (Sklenar et al., 2019). Dispersal is anemochorous, the pappus allowing achenes to travel several metres. Most species are long‑lived perennials with a rosette stage; clonal growth via rhizomes occurs in several high‑elevation taxa (Nesom, 1994).

Molecular phylogenies consistently place Roldana as a monophyletic clade within subtribe Senecioninae, separate from the core Senecio group (Sklenar et al., 2019). The genus is split into a “core” clade (sections Roldana and Hirsu) and a “Phoenicea” clade formerly treated as Cacalia sect. Roldana (Nesom, 1994). Recent synonymizations reduced Cacalia, and checklists retain Roldana in its circumscription (POWO, 2024). Alternative Senecio sensu lato concepts lack support from sequence data (Sklenar et al., 2019).

Several species, notably Roldana barbeyi and Roldana ligustrina, are cultivated as ornamentals with yellow inflorescences, and their fibrous roots aid slope stabilization; naturalized populations occur in southwestern US (GBIF, 2023) but none are invasive. No Roldana species are used as food or timber. Habitat loss, deforestation of pine‑oak forests, threatens endemic taxa; many lack IUCN assessments, indicating a gap. Work should integrate phylogenomics with surveys to prioritize habitats and model climate‑change impacts on mountain ecosystems (Sklenar et al., 2019).

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