Jasminocereus thouarsii

Accepted name and former varieties

Plants of the World Online accepts Jasminocereus thouarsii as the only species of the genus. Its original name is Cereus thouarsii F.A.C.Weber, published in 1899. The combination in Jasminocereus dates from 1959. The former names J. galapagensis, J. howellii and J. sclerocarpus are synonyms in this treatment. POWO recognises no accepted lower-rank taxa. [2-WWW]

The Charles Darwin Foundation retains the historical division into three varieties in its distribution description. It associates var. sclerocarpus with Isabela and Fernandina, var. thouarsii with San Cristóbal and Floreana, and var. delicatus with Santiago and Santa Cruz. In the atlas, these names link to one species. Alongside study results, they still identify material origin, allowing actual differences between islands to be retained. [24-WWW] [2-WWW]

Trunk, constrictions and branch surface

The adult plant has a distinct cylindrical trunk and branched upper part. Constrictions separating successive growth sections are visible on the branches. Stöcklin gives a height of up to around 7 m. The Charles Darwin Foundation's 2025 guide describes plants up to 5 m, while Britton and Rose's older monograph, under J. galapagensis, also recorded specimens around 8 m or taller. The descriptions represent different material and account scopes. [Stöcklin 2009, Stöcklin, p. 42. Britton and Rose, pp. 146–147. Guide, p. 86] [Britton and Rose 1920, Stöcklin, p. 42. Britton and Rose, pp. 146–147. Guide, p. 86] [Jaramillo Díaz et al. 2025, Stöcklin, p. 42. Britton and Rose, pp. 146–147. Guide, p. 86]

Britton and Rose described thick branches with 15–18 low ribs separated by broad, rounded grooves. Areoles were closely spaced and contained brown felt and numerous thin, sometimes bristle-like spines. The modern local flora guide gives areoles around 5 mm in diameter with 8–21 spines 0.8–6 cm long. The monograph's numbers concern material called J. galapagensis there, while the guide's data concern its own species description. [Britton and Rose 1920, pp. 147 and 86] [Jaramillo Díaz et al. 2025, pp. 147 and 86]

Slender tube, broad perianth and fruits

In the original genus description, the narrow floral tube opens into a widely spreading perianth. Stamens and style project towards its outer part. The lower flower region surrounding the ovary is covered with small scales. Britton and Rose described flowers of varying size and noted their variation even in the archipelago's early collections. [Britton and Rose 1920, p. 146–147]

For the Santa Cruz population (called J. thouarsii var. delicatus in the study), Jaramillo and colleagues cited a description of yellowish flowers 6–8 cm in diameter, with numerous stamens. The fruits of this form were reddish purple. The former description of J. galapagensis included greenish fruits. [Jaramillo et al. 2010, Jaramillo et al., p. 22. Britton and Rose, p. 147] [Britton and Rose 1920, Jaramillo et al., p. 22. Britton and Rose, p. 147]

The islands' dry zone and rainfall variability

The species is endemic to the Galápagos. The Charles Darwin Foundation database lists six islands and several islets. It mainly occupies the dry lowland zone and coasts. Evans and Macri studied plants above the coastal belt, often on raised volcanic rocks with sparse vegetation. Within the same zone, denser scrub can shelter stems and alter their light exposure. [24-WWW] [Evans and Macri 2008, Evans and Macri, p. 477]

The reproductive study site near the Charles Darwin station on Santa Cruz shows the importance of variation between years. The study gave mean annual rainfall of 620 mm for 1982–2002, with 2768 mm in 1983 and 63 mm in 1985. During the actual observations, 2001 was dry, with 293 mm of rain, and 2002 closer to average, with 577 mm. The numbers characterise local weather measurements. Germination experiments were linked to the problem of recruitment under such irregular water input. [Jaramillo et al. 2010, pp. 22–24]

Morning flowering and pollen transfer

In observations on Santa Cruz in 2001 and 2002, flowers opened after 5.30 and closed by 10.00 local time. The phenology study included 25 flowers on ten marked plants. The morning rhythm found in this population adds an important detail to older general descriptions of nocturnal flowering. [Jaramillo et al. 2010, pp. 22, 24]

Separate visitation observations on two plants recorded 800 insect visits. The endemic bee Xylocopa darwini accounted for 54% of visits, the introduced fly Acrosticta apicalis for 34%, and the endemic ant Camponotus planus for 12%. These proportions represent visit frequency. The effectiveness of a single visit by each species was not compared in a separate experiment. [Jaramillo et al. 2010, pp. 22–23]

Ten buds on five plants were enclosed in bags excluding visitors, while ten buds on another five plants remained freely accessible. Isolated flowers produced no fruit. All control flowers fruited, and the mean seed number was 325 per fruit, with a standard error of 15.3 and a sample of ten fruits. The result indicates the need for pollen transfer by an external agent. Self-compatibility remains unresolved because controlled pollination with self and foreign pollen was not performed. [Jaramillo et al. 2010, pp. 22, 24]

Germination and young plant development

The seed experiment included four treatments, each with three replicates of one hundred seeds. Soaking for 24 hours at 25°C or 60°C, followed by placing seeds on moist filter paper, was compared with unsoaked seeds on moist soil or filter paper. Containers stood beside a laboratory window for four months, without supplementary light or heat. Germination on soil averaged 7.3%, compared with 66.7% on filter paper without soaking. Soaked treatments yielded 52.0% and 47.3%. [Jaramillo et al. 2010, p. 22, Table 2 on p. 24]

In the authors' analysis, the soil treatment differed from the others. No significant difference in final germination was shown among the three filter-paper treatments. The result is associated with substrate conditions and moisture retention. The soaking treatments tested describe the experiment's scope, rather than an established method for improving germination in this species. [Jaramillo et al. 2010, p. 24, Table 2]

After reaching 5 mm, seedlings were transplanted into soil, watered regularly and measured until April 2002. After eleven months, their heights ranged from 9–25 mm. The table gave mortality of 30–48%, depending on prior seed treatment. Germination and seedling maintenance are therefore two separate stages. The Charles Darwin Foundation's 2025 guide emphasised moisture control during early development because excess water can be associated with embryo rotting and death. Comparison of experiments and nursery practice is explored in the article on population renewal. [Jaramillo et al. 2010, Jaramillo et al., pp. 22, 24. Guide, p. 86] [Jaramillo Díaz et al. 2025, Jaramillo et al., pp. 22, 24. Guide, p. 86]

Stem surface and exposure direction

Evans and Macri assessed 131 plants on Santa Cruz (var. delicatus in the publication) and 128 on San Cristóbal (var. thouarsii). They estimated coverage of the grooves between ribs by waxy changes and brown coverings termed scale and bark. On Santa Cruz, the mean excess of changes on eastern and western sides over northern and southern sides ranged around 1.2–1.7-fold across successive classes. On San Cristóbal, the ratio remained close to 1.1. [Evans and Macri 2008, p. 477, Table 2 on p. 480]

The sample included plants selected by exposure and severity criteria. Specimens without changes, those completely covered by the brown layer and heavily shaded ones were excluded. The authors suggested an influence of denser vegetation on San Cristóbal but did not assess it quantitatively. The overall ratio of around 1.4 given in the abstract concerns the full set of four species from the Galápagos and mainland Ecuador. Details are explained in the article on directional surface changes. [Evans and Macri 2008, p. 475, 477, 480–481]

Decaying branches as an insect habitat

In 2025, Sinclair described the fly Pareuxesta mathisi of the family Ulidiidae, reared from decaying branches of Jasminocereus. The Charles Darwin Foundation reports this insect on Floreana, Isabela and San Cristóbal. The documentation concerns dead, decaying material, rather than feeding inside a living stem or participation in flower pollination. [Sinclair 2025] [24-WWW]

Related articles

Materials from the author's archive

The species also appears in Konrad Szychowski's private material archive. [Kreuzinger 1935, file p. 16]