Ruschia indurata (L.Bolus) Schwantes

Klak, Cornelia, Hanáček, Pavel & Bruyns, Peter V., 2023, Six new species of Ruschieae (Aizoaceae) and further notes in Ruschia, South African Journal of Botany 156, pp. 144-161 : 153-156

3.2. Correction of lectotypification of Ruschia indurata (L.Bolus) Schwantes

Louisa Bolus (1922: 136) based her protologue for R. indurata on three different collections, all of which had been cultivated at Kirstenbosch for several years. An illustration was made by Mary Page in November 1917 of the type, showing a single clump, but citing all three collections at the top of this drawing as the voucher ( Fig. 12 ). Noteworthy is that the three collections came from three widely separated localities. One is from the Western Cape, at Beaufort West (Mathews sub NBG 2393/17). The other two are from the Eastern Cape, from Steytlerville (E. Pillans sub NBG 383/16) and from Steynsburg (H. de Villiers sub NBG 266/16).

Hartmann (1999: 53) indicated Pillans’ collection from Steytlerville as the lectotype. However, neither Pillans’ nor de Villiers’ collections are in the Bolus Herbarium. Only one of the three syntypes, the collection by Mathews ( Fig. 11 ), is in the Bolus Herbarium. An annotation on this sheet indicates that Hartmann selected this collection as the lectotype in 1995. We therefore conclude that Pillans’ collection was cited in error by Hartmann (1999).

Recent field work in the Beaufort West area suggests that Ruschia indurata is a rare species, endemic to certain calcritic pavements on the floor of the valley. So far, only a few localities within the same calcrete formation near Beaufort West are known where this species occurs.

Ruschia indurata is one of several dwarf succulent species in subgenus Ruschia , which are characterized by enclosed internodes, leaves that are toothy towards their apices and 5-locular capsules where the interior of the capsule disintegrates, so that soon only five pungent bundles remain on the stalk and project above the plant ( Fig. 13A ).

Bolus (1931: 241) noted that Ruschia pulvinaris , which was based on the gathering R. du Plessis sub NBG 2004/29 from Steynsburg, is very similar to R. indurata . The overall dimensions of the two species are superficially similar, but R. indurata differs from Ruschia pulvinaris by its more compact habit ( Fig. 13A, B ) and its smaller leaves (4-8 (-10) mm long in R. indurata , to 13 mm long in R. pulvinaris ). Although plants of R. pulvinaris also form cushions, these cushions are much larger and older plants often spread to 50 cm diam. ( Fig. 13D ). Noteworthy is also the difference in the color of the leaves, which is a glaucous-green in R. pulvinaris as opposed to whitish-grey in R. indurata . The whitish-grey color of the leaves is typical for several species in the tribe Ruschieae that are endemic to calcretes and limestones (e.g. Antimima lawsonii (L.Bolus) H.E.K.Hartmann , Lampranthus ceriseus (L.Bolus) L.Bolus and Ruschia calcicola (L.Bolus) L. Bolus ).

Ruschia pulvinaris grows in shallow soil overlying slabs of shale at altitudes of around 1450-1460 m a.s.l. (higher than the 900 m a.s.l. recorded for R. indurata ). Despite superficial similarities, the two species show important differences in their ecological niches.

Closely related is also Ruschia rigens L.Bolus , from the Bloemfontein area in the Free State. This shares the characteristics of the leaves and inflorescences, but forms more substantial cushions to 15 cm tall and has longer and thicker leaves, 25-30 X to 4 mm. All three species flower from late spring into summer, from October to December.

Our field work around Beaufort West and an investigation of herbarium specimens at BOL and NBG show that no similar species to R. indurata have been recorded from this area. We therefore conclude that the application of the name R. indurata must refer to the species which is endemic to the calcretes near Beaufort West. We believe that Bolus was mistaken that the collection from Steynsburg is the same as that from Beaufort West. As Pillans’ collection from Steytlerville is not at BOL, the identity of the species remains uncertain and requires further investigation.

Due to the confusion surrounding this species, we provide a detailed description below.

Ruschia indurata (L.Bolus) Schwantes , Z. Sukkulentenk. 2: 187 (1926).

Mesembryanthemum induratum L.Bolus , Ann. Bolus Herb. 3: 135 (1922).

Lectotype (cited erroneously by Hartmann in 1999 in Bradleya 17: 53 and corrected here): [ South Africa, Western Cape], Beaufort West , 1917, J.W. Mathews sub NBG 2393/17 ( BOL!, barcode BOL134738 , Fig. 11 ) .

Densely branched dwarf succulent forming low cushions 3-5 X 5-12 cm, becoming woody at base, internodes not visible. Leaves opposite, grey, trigonous, fused into a sheath to 1 mm long, free parts spreading, keeled on the back, 4-8 mm long, ± 2 mm broad and thick, with 1 conspicuous tooth below the apex, tips pointed, epidermis smooth and with dark dots below surface. Flowers solitary, pink, to 15 mm diam., almost sessile, pedicel to 5.5 mm long, calyx lobes 5, to 3 mm long, about equal length, 2 slightly succulent, petaloid staminodes in 2 rows, to 6.5 X 0.7 mm, filamentous staminodes in 2 rows, 3.5-4 X 0.5 mm, filamentous staminodes and stamens free to bases, of about equal length and collected into cone around center, with hair-like papillae in lower third, pollen yellow, stigmas 5, slender, yellow-green, ± 3.5 mm long, nectary a distinctly green crenulated ring. Capsule 5-locular, interior disintegrating so that only five pungent bundles on persistent fruit stalk remain and project above the plant, ± 6 mm diam., rims raised to ± 1 mm, lower part funnel-shaped, to 3 mm deep, covering membranes flexible, with distinct ledge below, keels slender, short, diverging and not touching at bases, valves opening into erect position, closing bodies hook-shaped, valve wings absent. Seeds ochre, ± 0.9 X 0.7-0.8 mm, somewhat D- shaped, almost smooth.

3.2.1. Distribution and ecology

Ruschia indurata is restricted to pavements of calcrete near Beaufort West, in the Western Cape ( Fig. 14 ), at around 900 m a.s.l. Flowering is from November to December.

3.2.2. Distinguishing features and relationships

Ruschia indurata is a highly compact dwarf succulent which forms a dense cushion in which the internodes are not visible on the branches ( Fig. 13A, B ). The leaves persist and are whitish grey. Ruschia indurata is related to R. rigens L. Bolus and R. pulvinaris L.Bolus and all three species are characterized by triquetrous, sharply pointed leaves, with a conspicuous subapical tooth. In all three the flowers are solitary and the fruits soon fall out of their bases after ripening, leaving the firm stalk and five pungent bundles projecting above the plant in their places. Ruschia indurata is the smallest in stature of these three species (see discussion above).

3.2.3. Conservation status

The area where Ruschia indurata occurs is threatened by the extension of an additional Eskom Powerline. Due to the highly specialized habitat, the proximity to Beaufort West and subsequent urbanization, we recommend a status of threatened.

3.2.4. Additional specimens investigated

South Africa. WESTERN CAPE: Beaufort West (3222): Farm Steenbokkies (-BC), 10 Jan. 2013, 890 m a.s.l., Klak 2171 ( BOL) .

Figures

Fig. 12. Illustration of Ruschia indurata (Mesembryanthemum induratum). Here three collections are cited (top corner), as in the protologue. Artist: M.M.Page.

Fig. 11. Lectotype of Ruschia indurata designated by H.E.K.Hartmann on 22nd June 1995. Collection by J.W.Mathews sub NBG 2393/17 (barcode BOL134738) made at Beaufort West.

Fig. 13. Habit of Ruschia indurata (A, B) and R.pulvinaris (C, D).Ruschia indurata forms dense cushions only, occasionally with short side branches extending beyond the cushion (A), whereas old plants of R.pulvinaris may spread and form extensive, much laxer cushions (D).

Fig. 14. Distribution of Ruschia indurata (square) and R. lawsonii (circle). Missing syntype collections of R. indurata, which are likely to refer to other species, are indicated: H.de Villiers sub NBG 266/16 from Steynsburg (triangle) and E.Pillans sub NBG 383/16 from Steytlerville (star).