Aeonium simsii

Aeonium simsii holds a unique distinction in its genus: it is the only species of Aeonium in which individual rosettes can flower more than once and survive. In every other member of the genus — all 37-odd species across Macaronesia, Morocco, East Africa, and Arabia — each rosette is strictly monocarpic, flowering once and then dying. This remarkable exception to the universal rule makes Aeonium simsii a plant of exceptional botanical interest. Endemic to the central and south-central highlands of Gran Canaria, this low-growing, densely clumping succulent perennial in the family Crassulaceae (subfamily Sempervivoideae, tribe Aeonieae) resembles a Sempervivum more than a typical tree-forming aeonium. Its compact habit, distinctive striped leaves, and flat-topped yellow inflorescences set it apart from every other member of the genus, while its polycarpic flowering strategy raises fascinating questions about the evolution of life-history traits in island succulent radiations.

Taxonomy and Etymology

Aeonium simsii (Sweet) Stearn is the accepted name according to POWO (Plants of the World Online). The species was originally described as Sempervivum simsii by Robert Sweet in Hortus Botanicus Vindobonensis (p. 230, 1818). The combination in Aeonium was made by William Thomas Stearn in The Gardeners’ Chronicle (ser. 3, 130: 169, 1951). Cristini’s 2022 revision of the genus (Piante Grasse 42, Supplement) provides the most recent comprehensive treatment.

POWO recognizes seven synonyms, reflecting the early taxonomic confusion surrounding this unusual plant:

  • Sempervivum simsii Sweet (1818) — the basionym.
  • Sempervivum ciliatum Sims (Botanical Magazine 45: t. 1978, 1818) — nom. illeg., a later homonym of Willdenow’s 1809 name for the Tenerife species now known as Aeonium ciliatum.
  • Sempervivum ciliare Haw. (1821)
  • Sempervivum caespitosum C.Sm. ex Link (1822)
  • Sempervivum ligulare Haw. (1821)
  • Aeonium caespitosum (C.Sm. ex Link) Webb & Berthel. (1840)
  • Sempervivum poculiforme A.Berger ex De Wild. (1909)

The genus name Aeonium derives from the Greek aionios (“ageless”). The specific epithet simsii honors John Sims (1749–1831), the English physician and botanist who served as editor of Curtis’s Botanical Magazine from 1801 to 1826 and who first illustrated the species (under the illegitimate name Sempervivum ciliatum) in that publication.

The sectional placement of Aeonium simsii within the genus is somewhat isolated. Its polycarpic habit, low-growing form, and distinctive leaf striping set it apart morphologically from all other sections. It has sometimes been associated with the broader Gran Canaria species assemblage in informal groupings, but its unique life-history trait suggests a deeply divergent evolutionary pathway within the genus.

Botanical Description

Aeonium simsii is a succulent perennial (classified by POWO as a perennial rather than as a subshrub, reflecting its low, mat-forming growth). It forms dense, spreading clumps of short, stout branches, typically reaching only 20 to 30 centimeters in height and spreading to form extensive mats. The overall appearance is strongly reminiscent of a Sempervivum (houseleek) — a ground-hugging rosette plant — rather than the tall, arborescent habit characteristic of most Aeonium species. This resemblance to mainland European houseleeks is immediately striking and is one of the plant’s most frequently noted features.

The leaves are arranged in cup-shaped to slightly flattened terminal rosettes measuring up to 12 centimeters in diameter. Each leaf is thick, fleshy, lance-shaped with a pointed tip (strap-shaped, according to some descriptions), up to 6 centimeters long and 2 centimeters wide, with a bright yellowish-green upper surface. The most distinctive foliar character is the presence of numerous short, dark green to brownish longitudinal stripes on the lower (abaxial) leaf surface, visible when the rosette is viewed from below or when individual leaves are turned over. The upper surface may sometimes display a purplish-brown median line. The leaf margins are lined with translucent, conical cilia, giving the rosettes a delicately fringed appearance.

The inflorescence is modest in size compared to the large panicles of tree aeoniums, emerging on a densely leafy stalk up to 30 centimeters tall. The flower cluster is flat-topped or nearly so — an unusual inflorescence shape within Aeonium, where conical, dome-shaped, or pyramidal panicles are the norm. The flowers are 7- to 9-merous, star-shaped, and bright yellow. Flowering occurs in spring.

The Polycarpic Exception

The most extraordinary feature of Aeonium simsii is its polycarpic flowering strategy. In all other Aeonium species, each individual rosette is monocarpic: it produces a single terminal inflorescence and then dies, with the plant persisting only through surviving non-flowering branches. In Aeonium simsii, by contrast, a rosette can produce an inflorescence, set seed, and then continue to grow, potentially flowering again in subsequent seasons. This makes it the sole polycarpic species in the entire genus — a biological anomaly that has attracted considerable scientific attention.

This polycarpic habit may be related to the species’ low-growing, clumping growth form and its high-altitude habitat on Gran Canaria, where environmental conditions (lower temperatures, shorter growing seasons, more unpredictable conditions) may favor iteroparous reproduction (multiple reproductive events over a lifetime) over the semelparous strategy (single, terminal reproduction) adopted by all other aeoniums. The evolutionary significance of this trait remains an active area of inquiry.

Natural Habitat and Ecology

Aeonium simsii is endemic to the island of Gran Canaria, specifically the central and south-central highlands. According to POWO, its native range covers central and south-central Gran Canaria. It grows in rocky sites at relatively high elevations: from approximately 500 to 1,900 meters above sea level, making it one of the highest-altitude aeoniums in the Canary Islands. The upper limit of its range (nearly 1,900 meters) approaches the summit of Gran Canaria and places the species in the Canarian pine forest (Pinus canariensis) zone, where it grows on rocky outcrops, cliff faces, and open ground within the pine woodland.

The high-altitude, montane habitat of Aeonium simsii is cooler, wetter, and more seasonal than the lowland subtropical environments occupied by species like Aeonium arboreum. These conditions — including regular frost at the highest stations — may have contributed to the evolution of the species’ compact, ground-hugging habit and its unique polycarpic strategy.

On Gran Canaria, Aeonium simsii co-occurs with other island endemics and hybridizes with at least two of them: Aeonium × velutinum (with Aeonium canariense) and Aeonium × lidii (with Aeonium percarneum).

The species is not currently assessed on the IUCN Red List. Its genome size has been estimated at 2C = approximately 1.1–1.2 pg (Suda et al., 2005; Frontiers in Ecology and Evolution, 2021), placing it among the smaller-genomed species in the genus.

Cultivation and Care

Aeonium simsii is occasionally available from specialist succulent nurseries and is well suited to container culture, rock gardens, and alpine troughs. Its compact, ground-covering habit and high-altitude provenance make it more cold-tolerant than many aeoniums, suited to USDA zones 9a to 11b. Brief frosts to approximately −6 °C (21 °F) may be tolerated in dry conditions, though this needs verification with individual plants and microclimates. Its high-altitude adaptation makes it more tolerant of cool winter temperatures than lowland species.

Exposure. Full sun to dappled shade. In its native pine forest habitat, the species receives filtered light under an open canopy. Full sun produces the best compact rosette form and the most vivid leaf striping.

Substrate. A well-drained, gritty mix is essential. A blend of approximately 70% mineral aggregate (pumice, volcanic grit, coarse sand) and 30% potting soil suits the species’ high-altitude, rocky native substrate. Excellent drainage is paramount given the species’ montane provenance.

Watering. Winter grower with summer semi-dormancy, though its high-altitude habitat means it is more tolerant of cool-season moisture than lowland species. Water regularly from autumn through spring. Reduce watering in summer but do not allow the mat of rosettes to dry out completely.

Fertilization. Dilute balanced liquid fertilizer applied sparingly two to three times during the active growing season.

Propagation

Stem cuttings and division are the primary methods. The densely clumping habit provides abundant material for division: gently separate a portion of the mat with attached roots and replant. Individual rosettes with a short stem section root readily.

Seed propagation is possible and straightforward. The species’ polycarpic habit means that individual rosettes can produce seed in multiple seasons without dying, potentially yielding more abundant seed than monocarpic species.

Pests and Diseases

Standard aeonium vulnerabilities apply: root rot from overwatering, mealybugs in rosette centers, and aphids on flower stalks. The dense, mat-forming habit can trap moisture and debris at the base of the rosettes, so good air circulation and a very free-draining substrate are particularly important.

Ornamental Interest and Uses

Aeonium simsii offers a completely different aesthetic from the tall, sculptural tree aeoniums that dominate gardens and collections. Its low, spreading, Sempervivum-like mats of cup-shaped rosettes with delicately fringed margins and striped undersides create a fine-textured groundcover effect that is unique within the genus. The flat-topped yellow flower clusters in spring add cheerful, modest-scale blooms perfectly proportioned to the plant’s compact size.

It is ideally suited to alpine troughs, rock gardens, green roofs (in frost-free climates), stone walls, and containers where its mat-forming habit can be displayed to advantage. For the collector, the biological fascination of the genus’ only polycarpic species — flowering, surviving, and flowering again — adds a layer of scientific interest that few other succulents can match.

The species is considered non-toxic, deer resistant, and salt tolerant.

Authority Sites

Bibliography

  • Sims, J. (1818). [Sempervivum ciliatum, nom. illeg.]. Curtis’s Botanical Magazine, 45: t. 1978. [First illustration.]
  • Sweet, R. (1818). [Sempervivum simsii]. Hortus Botanicus Vindobonensis, p. 230. [Basionym.]
  • Haworth, A.H. (1821). [Sempervivum ciliare, S. ligulare]. Saxifragearum Enumeratio, 2: 64.
  • Link, H.F. (1822). [Sempervivum caespitosum]. Enumeratio Plantarum Horti Regii Botanici Berolinensis Altera, 2: 20.
  • Webb, P.B. & Berthelot, S. (1840). [Aeonium caespitosum]. Histoire Naturelle des Îles Canaries, 3(2; 1): 191.
  • Berger, A. ex De Wildeman, É. (1909). [Sempervivum poculiforme]. Icones Horti Thenensis: t. 234.
  • Praeger, R.L. (1932). An Account of the Sempervivum Group. Royal Irish Academy, Dublin.
  • Stearn, W.T. (1951). [Aeonium simsii]. The Gardeners’ Chronicle, ser. 3, 130: 169. [Combination in Aeonium.]
  • Liu, H.-Y. (1989). Systematics of Aeonium (Crassulaceae). NMNS Taiwan Special Publication, 3: 1–102.
  • Govaerts, R. (1995). World Checklist of Seed Plants, 1(1, 2): 1–483, 529. MIM, Deurne.
  • Mes, T.H.M. & ‘t Hart, H. (1996). The evolution of growth forms in the Macaronesian genus Aeonium (Crassulaceae) inferred from chloroplast DNA RFLPs and morphology. Molecular Ecology, 5: 351–363.
  • Mort, M.E., Soltis, D.E., Soltis, P.S., Francisco-Ortega, J. & Santos-Guerra, A. (2002). Phylogenetics and evolution of the Macaronesian clade of Crassulaceae inferred from nuclear and chloroplast sequence data. Systematic Botany, 27(2): 271–288.
  • Suda, J., Kyncl, T. & Jarolímová, V. (2005). Genome size variation in Macaronesian angiosperms: forty percent of the Canarian endemic flora completed. Plant Systematics and Evolution, 252: 215–238.
  • Dobignard, A. & Chatelain, C. (2011). Index synonymique de la flore d’Afrique du Nord, vol. 3: 1–449. Éditions des Conservatoire et Jardin botaniques, Genève.
  • Bramwell, D. & Bramwell, Z. (2001). Wild Flowers of the Canary Islands. 2nd edition. Editorial Rueda, Madrid.
  • Cristini, M. (2022). The genus Aeonium. Piante Grasse, 42 (Supplement): 1–225.
  • Frontiers in Ecology and Evolution (2021). Diversification of Aeonium Species Across Macaronesian Archipelagos: Correlations Between Genome-Size Variation and Their Conservation Status. Frontiers in Ecology and Evolution, 9: 607338.