Rimacactus
From M&J Cactus Wiki
| Rimacactus | |
|---|---|
| File:Rimacactus laui.jpg | |
| Kingdom | Plantae |
| Family | Cactaceae |
| Subfamily | Cactoideae |
| Tribe | Notocacteae |
| SubTribe | Notocactinae |
| Genus | Rimacactus |
| Species | |
| Notes | Taxonomy follows Joël Lodé (2015) with reference to Mottram (2001), Nyffeler & Eggli (2010), and Faúndez & Kiesling (2007). |
Etymology
The name means "crevice cactus", referring to its growth in rock cracks and crevices.
Description
Rimacactus is a monotypic genus of extremely small, cryptic cacti adapted to hyper-arid environments.
- Habit: Solitary; globose to flattened; extremely small in habitat.
- Size: Typically 0.5–1 cm in diameter in the wild; larger in cultivation.
- Roots: Napiform (turnip-shaped), adapted for water storage.
- Stems: Almost completely hidden by dense trichomes.
- Areoles: Bearing long, white hairs obscuring the epidermis.
- Spines: Few, straight, relatively short.
- Leaves: Reported in seedlings, possibly representing early tubercles.
- Flowers: Diurnal but remaining open at night; disproportionately large relative to the plant; funnel-shaped.
- Flower color: Sulphur yellow with brownish outer tepals.
- Flower longevity: Very long-lasting (up to ~11 days).
- Pollination: Likely by small hymenopterans; extended flowering increases chances in pollinator-scarce environments.
- Fruits: Elongated, angled, hollow; dry at maturity; pinkish; persistent.
- Seeds: Black, shiny, pear-shaped; granular surface; sunken hilum.
- Seed dispersal: Likely myrmecochory (ant-mediated), possibly also wind-assisted.
Habitat
Occurs in one of the most extreme desert environments:
- rock crevices and fissures
- hyper-arid coastal desert zones
- areas influenced by fog (camanchaca)
Altitude range: approximately 400–1000 m.
Distribution
Chile:
- Antofagasta
Endemic to a very restricted area (~10 km²).
Taxonomy
A highly distinctive and historically controversial genus.
Key points:
- Discovered by Alfred Lau (1971)
- Initially associated with Eriosyce sensu lato (Nyffeler & Eggli, 1997)
- Separated as a distinct genus by Mottram (2001)
- Later transferred to Islaya by Faúndez & Kiesling (2007), but not retained in Lodé
- Molecular studies (Nyffeler & Eggli, 2010) confirm an isolated lineage
- Closely related to Neowerdermannia and Yavia
- Morphologically and anatomically distinct from Eriosyce, Islaya, and Matucana
Experimental hybridization showed compatibility with Oroya peruviana, but not with Copiapoa, Eriosyce, or Matucana.
The genus is therefore accepted as distinct in Lodé (2015).
Species
Monotypic genus:
Notes
- One of the smallest cacti in habitat.
- Extremely cryptic and easily overlooked in the wild.
- Adapted to ultra-arid conditions with fog-dependent moisture.
- Long-lived flowers compensate for scarce pollinators.
- Represents an isolated evolutionary lineage within Notocactinae.
