Aptosimum marlothii (Engl.) Hiern

Kolberg H., van Salgeren M. 2016. A synopsis of Aptosimum and Peliostomum (Scrophulariaceae) in Namibia, including the description of a new species, Aptosimum radiatum, and keys to all accepted species. Kew Bulletin 71:16. DOI 10.1007/S12225-016-9628-7

Type

Type: South Africa, Griqualand-West, Kimberley, Marloth 706 (lectotype PRE-158478!, selected here; isolectotypes BOL-138234!, K-410920!) — see Notes.

Morphology General Habit

Shrub, erect to decumbent, to 50 cm tall, lax, sparsely spinescent

Morphology Stem

Stems few, branched near base, ascending, 4 – 6 mm diam at base, 1 – 2 mm at tips, not densely leafy, glabrous at base to minutely glandular-pubescent at tips

Morphology Leaves

Leaves often clustered on short shoots, fleshy, linear-spathulate, sometimes slightly broader at apex, 5 – 10 × 1 – 2 mm, glabrous or sparingly short glandular-pilose towards base beneath; apex apiculate, scarcely acute; base sessile, somewhat narrowed; midrib weakly spinescent, spines sparse, obtusely subulate, spreading, slightly recurving, 2 – 10 mm long, glabrous; margins sparingly short pilose

Morphology Reproductive morphology Flowers

Flowers axillary or on short shoots, sessile to subsessile, pedicels 2 – 3 mm long

Morphology Reproductive morphology Flowers Calyx

Calyx lobed to middle at most, campanulate-tubular, 6 – 9 mm long, short stipitate-glandular and pubescent outside, conspicuously veined especially in fruit; tube to 6 mm long; lobes triangular, lanceolate to ovate, 2 – 3 mm long, apex acuminate

Morphology Reproductive morphology Flowers Corolla

Corolla 12 – 27 mm long, three times longer than calyx, shortly glandular-pilose outside; basal third of tube narrow, c. 5 × 1 mm, within calyx, distal part 10 – 22 mm long, whitish inside; lobes short obovate to circular, c. 4 × 4 mm, inside blue to purple

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens four, unequal, filaments of longer pair twice as long as those of shorter pair; anthers from almost equal in size up to those of shorter stamens being half the size of those of the longer pair of stamens, oblong-reniform, minutely puberulous to clearly ciliate

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary subglobose to obovoid; style filiform, thickened at distal 0.5 mm, bent at right angles below thickened part; stigma capitate

Morphology Reproductive morphology Fruits

Capsule subglobose, 7 – 12 mm diam., hispid or glabrous; apex weakly compressed and clearly emarginate

Morphology Reproductive morphology Seeds

Seeds irregularly obovoid, 1.2 × 1 mm, grey, densely and minutely tuberculate

Distribution

Africa: Namibia, South Africa.

Ecology

Occurring on calcareous soil near dry rivers or in depressions in the Kalahari sands and dwarf shrub savanna vegetation types (Mendelsohn et al. 2010). Reported in the Kalahari sands and Gordonia phytogeographical groups of Craven (2009). Altitude: 1200 – 1450 m.

Conservation

The evaluation for this species is LC (IUCN 2012, 2013) since under criterion B the AOO and EOO are just outside the thresholds for VU but no additional criteria qualifying it for VU nor any threats were observed. The species is evaluated as LC in South Africa (SANBI 2014).

Phenology

Flowering and fruiting throughout the year. Peak flowering: Sept. – April. Peak fruiting: Nov. – April.

Note

The specimen of Marloth 706 at PRE (PRE-158478) is selected here as lectotype because it is the most complete and copious specimen among the duplicates with a label in the collector’s handwriting.

This species is difficult to distinguish from Aptosimum spinescens (Thunb.) Emil Weber, especially if the habit is not described on the herbarium sheet. The sparser branching and lax stems are mentioned by Engler (1889: 251) as a character distinguishing these species. The sparser, thinner spinescent leaf midribs and larger capsules, however, tend to grade into A. spinescens. Detailed work over the species' entire distribution range is needed to establish if A. marlothii can be upheld.