Euphorbia schoenlandii

Stem and cyathium structure

Euphorbia schoenlandii Pax is a perennial stem succulent in the spurge family. It usually develops a single cylindrical stem, although branched plants also occur. Its surface bears prominent, spirally arranged, ovoid-conical tubercles. A triangular cavity lies just below the tip of each tubercle. A solitary woody spine grows from the upper part of this cavity and represents a modified sterile peduncle. Young spines are pale brown and become greyish or whitish with age [Jabar et al. 2024].

Fertile peduncles arise below the spines and carry solitary cyathia or groups of three cyathia. A cyathium is a group of highly reduced flowers enclosed within a common involucre, giving it the appearance of a single flower. In this species, the five glands along the involucre have toothed outer margins. The plant is monoecious, with male and female flowers on the same individual. Its smooth, three-chambered capsules turn deep red as they ripen [Jabar et al. 2024] [Lee et al. 2024].

Habitats and neighbouring shrubs

The species is endemic to the Western Cape Province of South Africa. It occurs in the southern Namaqualand Sandveld and neighbouring Knersvlakte within the Succulent Karoo biome. Rainfall is concentrated in the cooler part of the year, while coastal fog and dew supply additional moisture. The surveyed plants grew in sandy soils containing finer particles on low, gentle slopes. These field observations describe natural habitats and do not by themselves establish a potting-mix recipe [2-WWW] [Jabar et al. 2024].

In the study by Jabar and colleagues, 63% of the assessed plants were closely associated with shrubs, parts of which occurred within a 15 cm radius. The remaining 37% grew without such nearby vegetation. Shrubs can moderate temperature and reduce water loss in the surrounding microenvironment, leading the authors to consider their potential role as nurse plants. The study nevertheless documents an association. Seedling survival was not experimentally compared after adding or removing shelter, so the strength and mechanism of this facilitation remain to be tested [Jabar et al. 2024].

Flowering, insects and seeds

The literature places flowering between April and July, corresponding to autumn and winter in the Southern Hemisphere. During observations in 2015–2016, cyathia and fruits were recorded in May and in June and July. Fruits were present and dispersal was underway in September and October. Ripe capsules eject their seeds over short distances. This limited dispersal makes it difficult to restore connections between populations separated by transformed land [Jabar et al. 2024].

Cyathia were visited by ants, beetles, flies and thrips. Ants accounted for 78% of observed visits, and pollen was seen on individuals of Camponotus fulvopilosus. Pollen on an insect’s body indicates its potential to transport it. Pollination effectiveness nevertheless requires evidence that the insect delivers viable pollen to a stigma and contributes to seed production. The authors treat these visitors as potential pollinators, and the contributions of the different groups remain unresolved [Jabar et al. 2024].

Population abundance and recruitment

Using field surveys from 2015–2016, the authors estimated approximately 29 152 plants in the three populations surveyed. The largest, extensive population was divided into three zones for analysis. Abundance was calculated from density measurements and the area occupied because a complete count of every individual was impractical. This is an estimate tied to a defined survey period and coverage. It is not a current census of all surviving wild plants [Jabar et al. 2024].

The smallest adult size class predominated in all surveyed populations. This distribution may reflect episodic recruitment, with larger cohorts becoming established after favourable conditions. Stem size does not reveal an individual’s exact age, however, and the study does not reconstruct its germination date. No seedlings retaining cotyledons were found during the drought accompanying the surveys, although young plants occurred in some populations. The result describes limited recruitment at the time of measurement, alongside evidence of earlier establishment [Jabar et al. 2024].

Damage and habitat conservation

Larvae of the moth identified in the paper as Nephopteryx divisella were recorded in the surveyed populations. They fed near stem apices, damaged young spines and reproductive structures, and bored tunnels into the tissues. In the smallest surveyed population, feeding damage occurred on 47% of the assessed plants, whereas the proportions were lower elsewhere. This percentage refers to a particular sample and observation period. The presence of damage alone does not quantify the long-term population decline attributable to the insect [Jabar et al. 2024].

Documented threats included land transformation by mining and agriculture, and vegetation degradation associated with overgrazing. In 2024, the authors recommended retaining the Vulnerable category, VU, while updating the assessment criteria. This is the conclusion of that study, distinct from subsequent formal Red List updates. Protecting remaining habitat and its continuity matters for a species whose seeds disperse over short distances. A model predicting suitable habitat does not establish that the plant actually occurs there [Jabar et al. 2024].

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