Delosperma zeederbergii is only known from the upper Spekboom River between 1 500 and 2 000 m above sea level, growing on cliffs. It is found on the farm Doringhoek, about 5 km upstream from the bridge (Lydenburg Burgersfort Road) at about 1 500 m to 2 000 m at the Swartkop Forrel Oord. It was located on two separate occasions by the author in January 2005 and July 2022.

At the Swartkop Forrel Oord, at about 2 000 m altitude, plants were found in January 2005 on sheer south facing cliffs. The plant grows on ledges and shares its habitat with other species such as Aloe arborescens, Cotyledon orbiculata, Haemanthus humilis, Crassula lanceolata, Crassula sarcocaulis, Crassula setulosa var. deminuta, Senecio oxyriifolius, Plectranthus verticillatus. Taller shrubs in the habitat include Halleria lucida, Dais cotinifolia, Cephalanthus natalensis and Protea roupelliae. The associated vegetation is Lydenburg Mountain Grassland of the Grassland Biome (Mucina et al. 2006).

Fig. 4. The Spekboom River has cut a gorge through in the hard sandstone rock, forming the cliff-face habitat of Delosperma zeederbergii. Note the Helichrysum kraussii shrubs and occasional Cussonia paniculata var. sinuata in the grassland.

Along the Spekboom River, closer to the bridge, on the farm Doringhoek, plants were observed in July 2022 growing in Lydenburg Doringveld of the Grassland Biome (Mucina et al. 2006). The plants were observed on cliffs adjacent to the river on both sides. The cliff and rocky steep sides here with plants mostly a mosaic of the Savanna & Grassland biome and include species such as Berchemia discolor, Bowkeria cymosa, Ficus glumosa, Ficus burkei, Ficus sur, Ficus ingens, Ficus abutiilifolia, Greyia sutherlandii, Commiphora marlothii, Englerophytum magalismontanum, Cussonia spicata and Cussonia transvaalensis. On the cliffs, Delosperma zeederbergii shares its shallow crevice habitat with plants such as Aeollanthus buchnerianus, Aloe arborescens, Aloe spicata, Crassula expansa subsp. fragilis, Crassula setulosa, Crassula swaziensis, Haemanthus humilis, Cyanotis speciosa, Kalanchoe sexangularis, Kalanchoe rotundifolia, Plectranthus verticillatus, Coleus ramosior, Senecio barbertonicus and Senecio oxyriifolius.

Fig. 5. Left: The cliff-face habitat at Spekboom River, July 2022, although no spekboom (Portulacaria afra) grows here, Senecio barbertonicus and rock splitting figs (Ficus abutilifolia) also grow on the cliff. Right: Delosperma zeederbergii growing in a rock crack on an exposed north face. Note the shorter compact flat purplish brown leaves and seed capsules from the previous season.

Plants usually grow on mineral-poor, quarzitic sandstone cliffs. The aspect on the north and west face is exposed but the southern cliffs, where most plants grow, are protected from excessive sunlight and the rocks also hold the moisture longer. Plants are rooted in crevices of ledges, occasionally becoming drooping over the rock faces. Temperatures are moderate to cold in winter, the average daily maximum about 18°C and average daily minimum for the region 10°C. Winters are cool but frost is absent or light. Rainfall is mainly in summer, ranging from 800 to 1 500 mm per annum.