Holotypus: Madagascar. Reg. Amoron'i Mania [Prov. Fianarantsoa]: Ambositra, Ambalamanakana, Réserve Ankazomivady, inselberg côté droit de la route RN 7 vers Fianarantsoa, 20°46′22″S 47°10′51″E, 1706 m, 9.III.2016, fl. & fr., Rabarimanarivo, Porembski, Giebelmann & Werner 741 (TAN!; iso-: MO [MO-2894736]!).

Linderniella porembskii Andriamiar. & Rabarim. can be distinguished from the most similar L. horombensis (Eb. Fisch.) Eb. Fisch. et al. by its habit with dense and richly branched stems, decumbent to erect (vs. stems usually single, erect from a basal rosette), plants glabrous to glabrescent (vs. pubescent), and its capsules obovate-acuminate (vs. acuminate-attenuate).

Resurrection herbs, up to 4.5 cm high, tufted, decumbent to erect, glabrous to glabrescent. Stems somewhat succulent, 4-angled, glabrous to glabrescent (with sparse, short, stiff trichomes), highly branched from the base; young branches green (in vivo), adult branches brown to red (in vivo); lowest internode (from base to first node) about 1.5 cm long. Leaves somewhat succulent, densely foveate, glabrous to glabrescent, sometimes with sparse and short stiff white hairs at the margin, shortly petiolate; basal leaves 4–12 forming a rosette, spathulate, 9–14 × 1.5–2.5 mm, apex obtuse; upper leaves, opposite, lanceolate to obovate, 3.5–4 × 1–2 mm, sessile, base gradually tapering, apex acute to obtuse, sometimes slightly mucronate and reddish apically, margin entire, glabrous or sparsely pubescent with minute short stiff white hairs, veins palmate, obscurely visible abaxially, inconspicuous adaxially. Flowers solitary in the upper leaf axils, pedicellate, erect; pedicels 5–8 mm long, accrescent (up to 10 mm in fruit); calyx foveate, somewhat succulent, green with red lobe margins (in vivo), 3.4–4 mm long, glabrous, with 5 lobes up to 1 mm long, persistent in fruit; corolla white or light purple with purple shading on the throat, 8 mm long, tube 3.5 mm long, upper lip bifid, lower lip 3-lobed with sinuate margins; stamens 4, the abaxial pair reduced with curved and geniculate filaments 0.6 × 0.09 mm, anthers 0.2 mm long, the adaxial pair with straight filaments 0.7 × 0.25 mm long, anthers 0.5 mm long; pistil 4 mm long, style 3 mm long, stigma bilobed. Mature capsule distinctly longer than calyx lobes, obovoid acuminate, 6 mm long, dehiscent into two valves when dried or mature. Seeds bothrospermous, 0.6 mm long.

Etymology. – The species is named in honor of Prof. Dr. Stefan Porembski, who has studied inselbergs globally and made important contributions to our knowledge, understanding, and conservation of these unique ecosystems. He published many articles dealing with these subjects, including some that advocate for urgent protection of this neglected habitat (Porembski et al., 2016). He also participated in the collection of the type in 2016.

Distribution and ecology. – Linderniella porembskii is known from three granitic inselbergs in central Madagascar, at mid-elevations of c. 1500 – 1700 m (Madagascar Catalogue, 2023). It is restricted to rock outcrops. The species appears to be a resurrection plant growing in mats dominated by monocotyledonous, small patch-forming on open rock and shallow depressions.

Conservation status. – Linderniella porembskii is known from three recent collections made between 2015 and 2016. These three collections represent two subpopulations occurring outside the protected area network and are highly threatened by ongoing degradation or destruction of its habitat due to fire, quarrying, grazing, trampling by people overharvesting other plants (medicinal, ornamental, useful plants), adjacent farming, and climate change (Porembski et al., 2016). The species has both an estimated Extent of Occurrence [EOO] and a minimum Area of Occupancy [AOO] of 12 km2 falling within the limits for “Endangered” status under criterion B2. With respect to the most plausible threat of fire, the two known subpopulations represent two locations sensu Iucn (2012). In addition, it is inferred that the ongoing loss of its habitat induces a decline in its AOO, EOO, the extent and the quality of its habitat, the number of subpopulations, and the number of mature individuals. Based on available information, L. porembskii is preliminary assessed as “Endangered” [EN B1a b(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v)] according to IUCN Red List Categories and Criteria (Iucn, 2012).

Notes. – Linderniella porembskii resembles L. horombensis and L. pygmaea in general habit but it can be distinguished from both species by its dense and richly branched stems, which are decumbent to erect, by its glabrous calyx and its obovate-acuminate capsules (vs. erect, usually single stems arising from a basal rosette, pubescent calyx, and acuminate-attenuate capsules in L. pygmaea and L. horombensis). Linderniella porembskii and L. horombensis have foveate leaves and calyces, entire leaf margin, abaxial stamens and anthers reduced to staminodes. They can also be distinguished by the basal leaf size, pedicel length, and the plant pubescence of plants.

Specimens examined. – Madagascar. Reg. Amoron'i Mania [Prov. Fianarantsoa]: Ivato, Faliarivo Anjoman'Ankona, Bemanta, inselberg côté E de la route RN 35, à env. 13 km d'Ivato vers Ambatofinandrahana, 20°40′46″S 47°07′49″E, 1673 m, 14.XII.2015, fl., Rabarimanarivo et al. 615 (MO, TAN); ibid. loco, inselberg côté gauche de la route RN 35, sur la route vers le camp de Bemanta, 20°40′33″S 47°07′28″E, 1582 m, 8.III.2016, fl., Rabarimanarivo et al. 719 (MO, TAN).