Jacobsenia, L. Bolus & Schwantes

Klak, C., Hanáček, P. & Bruyns, P. V., 2018, A recircumscription of Jacobsenia (Aizoaceae): Re-instating Drosanthemopsis, with two new quartz-endemics from Namaqualand, South Africa and sinking Knersia *, South African Journal of Botany 116 (10), pp. 67-81 : 76

5.1. Jacobsenia

L. Bolus & Schwantes, Kakteen und andere Sukkulenten 5: 69 (1954).

Type: Jacobsenia kolbei (L.Bolus) L.Bolus & Schwantes.

Succulent perennial shrubs to 50 cm high or caespitose shrublets to 15 cm high, stems to 10 mm diam., young plants caespitose, adult plants either with erect long shoots and lateral short shoots, or plants compact without clear distinction between long and short shoots. Leaves succulent, opposite, fresh green, erect or spreading, terete or ±digitiform with upper surface flattened, lower surface slightly keeled, to 70 mm long and 10 mm diam., at least the last leaf-pair of the season persisting on the stem until the next season; leaf-pairs of a season isophyllous or slightly anisophyllous, basally connate for c. 1 / 5 of their length; epidermis with large bladder cells with thickened outer walls, elliptic to polygonal, smooth or with a hair-like central protrusion. Flowers terminal, solitary, emerging from the connate portion of the 2nd leaf-pair of the season, 60–80 mm diam., pedicels 10–70 mm long, sepals (4)5 or 6, petaloid staminodes in 4 or 5 rows, white, light yellow or rarely cerise, inner petals shorter, filamentous staminodes very few or absent, filaments white or yellow, papillate at bases; holonectary; Fruit a hygrochastic capsule, borderline between expanding keels and expanding sheets very indistinct; covering membranes covering more than ½ to ¾ of the locule, closing bodies absent, numerous sterile funicle in the upper part of the placenta; locules 5 or 6 (to 8), 8–17 mm diam. Seed s ochre to brown, testa minutely papillate, c. 0.7 × 0.5 mm.

Ecology and distribution: South Africa, south-western Namaqualand, between Vanrhynsdorp, Vredendal and Bitterfontein ( Fig. 7 ). In shallow rocky soils, also in reefs of schist, or on loamy strongly saline sand, with a cover of large quartz gravel.

Flowering occurs from July to September. The two species were found sympatrically in flower on the farm Kerskloof. The difference in flower colour suggests that they may have different pollinators but possible hybrids were noted there.

Diagnostic characters: Jacobsenia is characterized by the bladder cells in the epidermis of the leaves. These are much enlarged, usually protruding cells scattered among “normal” epidermal cells in a more or less regular pattern. They are apically thickened, elliptical to polygonal in outline and either smooth or with a central hair-like protrusion. Leaves in Jacobsenia (and equally in Drosanthemopsis ) are not deciduous and at least the last leaf-pair of the season persists until the first new leaf-pair of the next season begins to form. This is different to leaves in Dicrocaulon , Diplosoma Meyerophytum , Mitrophyllum , Monilaria and Oophytum , which dry out and form a persistent sheath over the apical bud.

Jacobsenia most closely resembles members of Drosanthemopsis , but differs by its fruits and by the sculpturing of the epidermis ( Table 1 ).

5.1.1. Key to Jacobsenia

1. Adult plants with erect long shoots bearing lateral short shoots, to 50 cm high, sepals 5, locules 5 ……………………………………… J. kolbei .

1.’ Adult plants compact without distinct long shoots, to 15 cm high, sepals 6, locules 6, rarely 5, 7 or 8…………………………………… J. hallii .

Figures

Fig. 7. Distribution of Jacobsenia. J.kolbei and J.hallii, with Knersvlakte phytochorion indicated (red hashes).