Pachycarpus acidostelma M.Glen & Nicholas
Common names: Highflats pachycarpus
Recognized by its creamy to pale yellow, saucer-shaped flowers, the elusive Pachycarpus acidostelma remains one of South Africa’s hidden gems.
Fig. 1. Pachycarpus acidostelma, cream coloured corolla and corona.
The perennial geophytic herb, Pachycarpus acidostelma, stands upright at 400 mm high, with milky latex, a firmly established rootstock and a slender, tube shaped caudex with a woody base.
The stems are simple and somewhat rough to the touch. The leaves are egg-shaped and broad, growing to about 35–80 × 20–35 mm long. The leaf apex is blunt with a minor projecting point. The leaf base gradually tapers and is curved. The leaf margins are thick, firm, sometimes slightly curved, with fine hairs. The lower surface of the midrib is covered with rigid hairs. Pronounced veins occur on the lower leaf surface. The leaf stalk is very short, growing to about 3.0–6.5 mm long.
Fig. 2. A plant and leaves of Pachycarpus acidostelma.
The inflorescence grows in a flat-topped flower cluster (corymbose), arising from the end of the stem with buds growing outside the axils, about 4 per stem. Inflorescence stalks are free, with about 4 to 6 flowers growing to about 10–30 mm in diameter. Flower stalks are covered in short, soft hairs that grow to about 15–21 mm long.
The flowers of Pachycarpus acidostelma are pleasantly scented, light cream to pastel yellow, 13–17 × 23–25 mm. The calyx is slightly rough to the touch and bent downwards, 7.5–9 × 3.5–6.5 mm. The corolla is saucer-shaped when young, with tips bending downwards with age. The corolla lobes are egg-shaped, 9–12 × 9 mm. The gynostegium (a compound organ in milkweeds, formed by the merging of the filaments and the style) grows up to 3.9–4.8 mm tall. The corona is cream in colour, with a touch of yellow at the base, 1.4–3.2 × 1.7–2.4 mm and 2.5–2.7 mm tall. The part of the corona near the point of attachment to the corolla is broad with two curved appendages attached. The appendages are 2–2.7 × 0.7–1.9 mm, toothed and deltoid, tapering to a sharp point. A narrow indentation occurs on the surface and between the appendages.
The anther appendages are oblong and sharply pointed, about 2 × 1.7–2 mm. The anther wings are somewhat pronounced, about 2.4–3.4 × 1–1.4 mm. The pollinarium has a small mass of about 0.75–0.85 × 0.45 mm, on which pollinators attach to during the pollination process. The translator arm (a distinctive structure of the subfamily Asclepiadoideae that connects the pollinia to the gland) is narrowly winged and about 0.9–1.4 mm in diameter. The pollinium is compressed, oblong, extends along the axis and is about 1.35–1.8 × 0.65–0.9 mm in diameter. The head of the style is about 3.3–3.7 mm in diameter.
Fig. 3. Pachycarpus acidostelma flowers.
The fruits of Pachycarpus acidostelma are single, egg-shaped, swollen follicles, growing up to 90 × 34 mm on a drooping flower stalk, winged and pointed at the tip of the flower stalk.
Pachycarpus aidostelma is currently assessed as Critically Endangered (CR) on the Red List of South African Plants. The species is restricted to one site in KwaZulu-Natal with an extent of occurrence of less than 1 km2. It is currently threatened by livestock grazing, competition with alien invasive species, habitat loss and degradation, urban and agricultural expansion and ineffective fire management systems.
The Custodians of Rare and Endangered Wildflowers (CREW) recently visited the type locality and observed a few plants in flower.
Distribution and habitat
Pachycarpus acidostelma is a South African endemic species found in the Midlands Mistbelt Grassland of KwaZulu-Natal, South Africa, at an altitude between 960 and 976 m, in one of the most threatened vegetation types, the KwaZulu-Natal Sandstone Sourveld. Pachycarpus acidostelma is considered to be a critical habitat species with only one remaining subpopulation in the wild.
Derivation of name and historical aspects
The genus name Pachycarpus originates from Greek words pachys, meaning ‘thick’ and karpos, meaning ‘fruit’. Pachycarpus is characterized by the large fruit borne to most species within the genus.
Pachycarpus acidostelma was first discovered in 2007 and was collected by Adam Shuttleworth in 2011, a plant ecologist from University of KwaZulu-Natal (UKZN). The species was later described by UKZN PhD student, Melissa Glen and Dr. Ashley Nicholas. Glen named the species Pachycarpus acidostelma meaning ‘sharply pointed crown’ in reference to the plant’s sharply pointed corona lobes.
Pachycarpus acidostelma is known to flower in midsummer (December) and can be distinguished from Pachycarpus scaber and Pachycarpus asperifolius by its small size, saucer-shaped corolla and triangular corona lobes that are sharply pointed.
Fig. 4. Interaction between beetles and ants on the flowers of Pachycarpus acidostelma.
Pachycarpus acidostelma is pollinated by Atrichelaphinis tigrina (chafer beetles). According to Shuttleworth (2018) the short corona lobes exude nectar that trickles down the sides of the gynostegium and is collected at the base of the corona lobes. The chafer beetles accumulate pollinaria on their tarsi when they visit the flowers of Pachycarpus acidostelma. Flesh flies, spider wasps and monkey beetles have also been observed on the flowers of Pachycarpus acidostelma, however, they are not likely to have significant impact on the pollination for the species.
As far as could be determined research on the uses of Pachycarpus acidostelma has not been conducted. However, many species of Pachycarpus are known to have medicinal properties that curb hunger; alleviate headaches, indigestion and stomach cramps; and treat dysentery, wounds, oedema, colic and diarrhea.
Growing Pachycarpus acidostelma
Like most species in this genus, Pachycarpus acidostelma would likely be difficult to propagate. Due to the threatened status of this species it is unlikely to be found in nurseries or be available for growing.
- Bester, S.P. 2008. Pachycarpus schinzianus (Schltr.) N.E.Br. (Apocynaceae). PlantZAfrica. Online. http://pza.sanbi.org/pachycarpus-schinzianus.
- Nkwanyana, M. & Bester, S.P. 2018. Pachycarpus campanulatus (Harv.) N.E.Br. var. campanulatus. (Apocynaceae). PlantZAfrica. Online. http://pza.sanbi.org/pachycarpus-campanulatus.
- Bester, S.P. 2017. Pachycarpus natalensis N.E.Br. (Apocynaceae). PlantZAfrica. Online. http://pza.sanbi.org/pachycarpus-natalensis.
- Glen, M., Nicholas, A. & Lamb, J. 2011. A new species of Pachycarpus (Apocynaceae: Asclepiadoideae) from KwaZulu-Natal, South Africa. Novon 21(4):426–430.
- Payet, C. 2014. Botanical discovery blooming lovely. Sunday Tribune. Online. https://www.pressreader.com/south-africa/sunday-tribune-south-africa/20140330/281986080518023.
- Shuttleworth, A. 2018. A penchant for Pachycarpus: an illustrated account of the pollination systems of the genus in South Africa. PlantLife SA 46(3). Online. http://plantlifesouthafrica.blogspot.com/2019/01/plantlife-sa-volume-463-december-2018.html?m=1.
- Von Staden, L. 2014. Pachycarpus acidostelma M.Glen & Nicholas. National Assessment: Red List of South African Plants version 2020.1. Accessed on 2021/11/17
Custodians for Rare and Endangered Wildflowers (CREW) – Summer Rainfall Region
Plant Type: Bulb, Perennial
SA Distribution: KwaZulu-Natal
Soil type: Sandy, Loam
Flowering season: Early Summer
Flower colour: Cream, Yellow
Aspect: Full Sun
Gardening skill: Challenging