Lacomucinaea lineata (Linneaus f.) Nickrent & M.A.García 2015

Nickrent, Daniel L. & García, Miguel A., 2015, Lacomucinaea, a new monotypic genus in Thesiaceae (Santalales), Phytotaxa 224 (2), pp. 173-184 : 180-182

Lacomucinaea lineata (Linneaus f.) Nickrent & M.A.García , comb. nov. ( Fig. 2 ).

Basionym: Thesium lineatum Linnaeus. (1782: 162) . Type:— SOUTH AFRICA. “Habitat in Cap. Bonae spei.”, C.P. Thunberg s.n.

(holotype UPS-THUNB 6035!). Thesium ephedroides A.W. Hill (1910: 183) . Type:— NAMIBIA. Kabub Mts., 1630 m, October 1906, P.T. Range 65 (holotype B!). Thesium viscibaccatum Dinter (1926: 452) . Type:— NAMIBIA. Klinghardt Gebirge, 26 September 1922, M.K. Dinter 4006 (holotype

PRE!).

Additional specimens examined: SOUTH AFRICA: Barrydale , hellig van de Warmwaterberg. Klipperige bodem, 21 Aug. 1971, E. Coppejans EC1016 ( BR) ; Van Rhynsdorp DA, SW trending rocky slopes above Wiedouw River , 5 Feb. 1982, P. Goldblatt 6526 ( BR) ; Along R354 , ca. 30 km north of Matjiesfontein, 29 Oct. 1996, D. L. Nickrent et al. 4088.5 ( SIU) ; Prieska District . About 3 km north west of Prieska, 3 Apr. 2000, P. Balkwill & L. McDade 11765 ( MO) ; Namaqualand , Bulletrap ( N of Springbok), 3–4 km on road to Nigramoep, 2 Sept. 2006, L. Mucina 020906/12 ( MA, NBG) ; 5.34 air km E of Middelplaas , 25 Nov. 2007, M. A. García et al. DLN 5388 ( MA, SIU, NBG) ; Hills above rest area along R 341 , ca. 3.6 air km S of Klaarstroom at Peraboom Drif, 27 Nov. 2007, M. A. García et al. DLN 5397 ( MA, SIU, NBG) . NAMIBIA: Lüderitz District . Farm Süd-Witpütz, Lavranos & Pehlemann 21691 ( MO) .

Description

Shrub to 2 m tall, densely branched, compact or spreading; bark on basal stems furrowed and ridged, grey to brown; young branches sometimes succulent, glabrous, glaucous, with yellow-green longitudinal striations that branch dichotomously and also anastomose. These striations later, following periderm growth, form the ridges on the bark of older branches. Shorter branches becoming spinose with age, with dry, tapering, pungent apices. Leaves alternate, simple, ciliolate when young, sparcely distributed on younger growth, petiole ca. 1/5 to 1/6 length of leaf, blade succulent, initially somewhat fusiform, terete, tapering more at the distal end, apex acute, 2–5 × 1 mm, caducous, progressively senescing on developmentally older stems, petiole and leaf apex senescing first, eventually followed by the middle portion of the leaf; leaf abscising leaving a persistent brown petiolar stub or sometimes as a whithered whole leaf; lateral branches subtended by one main bract and two transverse ones above. Flowers solitary, peduncle 1.5 mm long, subtended by a bract, at apex with two transversely oriented (with respect to bract), triangular to sublanceolate bracteoles, initially green, becoming brown and squamate, apex acuminate, senescing, margin ciliolate. Flower pedicel 1 mm long, merging gradually into the receptacle. Calyx not differentiated (fused to ovary and hypanthial cup), ca. 0.6 mm high, bearing a slightly raised, elliptic gland at lobe junctions. Corolla actinomorphic, (4)5-merous, 2.5–3.0 mm wide, corolla tube not present, lobes valvate, triangular, 1–1.5 mm long, uncinate, outer surface glabrous, inner surface without apical trichomes (beard), white. Stamens 5, antipetalous, inserted at junction of disk and corolla, at anthesis reaching only midway to corolla lobes, anther and filament each 0.4–0.5 mm long, anther subbasifixed, dithecal, tetrasporangiate, introrse, connected to corolla by post-staminal trichomes. Pollen heteropolar, tricolpate (see Fig. 4a in Stearn 1972). Disk lining hypanthium, at rim with distinct rounded lobes alternating with corolla lobes. Style filiform, ca. 0.8 mm long, stigma small, 2-lobed, lobes globose, positioned at ca. the height of the anthers. Ovary inferior, unilocular, placentation free-central with 3 pendulous ovules, placenta contorted with a peg-shaped projection at its apex. Fruit a drupe, pedunculate with persistent, scarious subtending bracteoles, white at maturity, globose to ellipsoid, 5–8 mm long, surface smooth, no reticulum visible, crowned by persistent, scarious, brown corolla lobes. Seed enclosed in a stony endocarp.

Lacomucinaea has a number of morphological features that are generally considered xeric adaptations. The glaucous stems are photosynthetic and, particularly on shorter axes, may become shoot spines such as those seen in Ulex Linnaeus (1753: 741 ; Fabaceae ). Both its leaves and distal stems are succulent. The caducous nature of its leaves, not seen in any other species in Thesiaceae , are reminiscent of this syndrome in succulents such as Opuntia subulata Engelmann (1883: 627 ; Cactaceae ) and some members of Euphorbia Linnaeus (1753: 450 ; Euphorbiaceae ). The striations that inspired the specific name of this plant are formed by cortical fibers that form long , raised ridges on the stems. Anatomically, these are primary phloem fiber bundles (not collenchyma as stated in Hendrych 1972), similar to the bast fibers seen in stems of flax ( Linum usitatissimum Linnaeus (1753: 277 ; Linaceae )). For Lacomucinaea and Osyridicarpos , these bundles are located in the cortex near the epidermis with a cushion of collenchyma in between. This arrangement is different from that seen in many South African Thesium with decurrent leaves where the primary phloem fiber bundles are located deep in the cortex near the vascular cambium. (Supplementary File S2).

Lacomucinaea is widely distributed in southern Africa ranging from central South Africa to Namibia ( Fig. 3 ). It has not been reported for Botswana ( Setshogo, 2005) but might be expected in the savanna biome in the southwestern part of that country. Examination of its distribution across biomes and bioregions of South Africa ( Mucina & Rutherford, 2006) shows it is most abundant in the Succulent Karoo and Nama-Karoo biomes. This plant is nearly absent in the Fynbos biome, with the exception of the Hantam Plateau Dolerite Renosterveld, part of the Granite and Dolerite Renosterveld Bioregion ( Mucina & Rutherford 2006). It is also known from the Great Fish Noorsveld vegetation unit of the Albany Thicket biome near Grahamstown.

Figures

FIGURE 2. Lacomucinaea lineata vegetative and reproductive features.A. Plant habit. B. Base of stem showing bark features. C. Young branches bearing succulent leaves with petioles beginning to senesce. D. Older branches showing further senescence of leaves which eventually yellow and abscise leaving a peg-like petiolar stub. E. The flowers, here in bud stage, are borne singly in the axils of leaves. F. Inflorescences with flower buds and a flower in anthesis (photo by Nicky van Berkel, used with permission). G. Flower in longitudinal section, showing the two subtending bracteoles and the lobed hypanthial disk. H. Shoot with young and mature fruits. I. Closer view of fruits showing smooth surface and persistent corolla lobes at apex.

FIGURE 3. Distribution of Lacomucinaea lineata obtained from 124 unique locations present on the GBIF herbarium record database. See Materials and Methods for sources of the biome maps for South Africa, Lesotho, Namibia, and Swaziland.