Portulaca trianthemoides Bremekamp (1933: 239–240)

Woodenberg, Wynston R., Govender, Yanadayalan & Ramdhani, Syd, 2024, Rediscovery of Portulaca trianthemoides (Portulacaceae) in southern Africa after 89 years, Phytotaxa 669 (2), pp. 131-140 : 134-138

Portulaca trianthemoides Bremekamp (1933: 239–240) .

Lectotype (designated here): — SOUTH AFRICA. Limpopo province, 2229CD, Zoutpansberg, Soutpan (west side of -), 21 January 1931, Bremekamp & Schweickherdt 231 ( PRE0403424 -0!).

Typification:— Bremekamp (1933: 239–240) validly described Portulaca trianthemoides by giving a detailed description. No herbarium was cited, but locus classicus as well as date of collection (“Loc. Zoutpan (Zoutpansberg). 21.I.31”) were provided. The occurrence of a date of collection allowed to consider Bremekamp’s statement as a syntype citation (Art. 9.6 of Shenzhen Code; Turland et al. 2018). We traced two specimens at PRE, viz. Bremekamp & Schweickherdt 231, which were collected on the 20 th and 21 st of January 1931, respectively. These two specimens were labelled as isotypes; however, their designation as such was not documented in the literature nor does a holotype exist based on an extensive search (these specimens may have been tentatively designated as isotypes in the past by the staff of the National Herbarium, PRE). Moreover, only the plant collected on 21 January can be considered for the lectotypification purpose, since this is the only day cited in the protologue. To note also that Bremekamp (1933: 233) stated that all the types of new species were deposited in the National Herbarium (PRE), Transvaal Museum Herbarium, and the herbarium at the University of Pretoria (specimens of the Transvaal Museum Herbarium are now housed at the National Herbarium).

According to Glen & Germishuizen (2010), Bremekamp returned to Holland in 1931 (the year in which he collected Portulaca trianthemoides ), and settled in Bilthoven (a village in Utrecht), where he worked at the Botanical Museum and Herbarium (Herbarium Vadense), which now forms part of the National Herbarium of the Netherlands (NHN). While all type specimens of the NHN comprising collections of Utrecht University, Wageningen University, and the Universiteit Leiden branches are available online (https://plants.jstor.org/partner/NHN), there are no specimens (type or otherwise) of P. trianthemoides . Furthermore, the only other specimen collected in 1934 (Schweickerdt & Verdoorn 458 at K), was not designated as a type. Therefore, in the absence of a known holotype it is necessary to select a lectotype.

All things considered, the only available specimen useful as lectotype is that collected on 21 st of January 1931.

Protologue description:— Bremekamp’s (1933: 239–240) description of Portulaca trianthemoides is quite detailed; however, it misses a few details of important characters. For example, the following characters were not mentioned: growth habit, plant height, branch length, hair length, involucral leaf number, number of flower buds in the inflorescence, flower size, presence of the sepal keel, petal shape and colour, as well as seed colour.

While the lectotype specimen ( Fig. 3 ) could be used to ascertain such characters as plant height and hair length, it would not be able to account for variation among plants growing in the population, and many of the other characters such as flower colour necessitated observation of living specimens in situ.

Emended description:— Erect to semi-erect annual succulent herb ± 150 mm high with single thin taproot and smaller side roots. Stems light green to purple (occasionally), with inconspicuous leaf axillary hairs, branching; branches up to 134 mm; leaf axillary hairs 0.2–0.6 mm long. Leaves green, succulent, numerous, narrowly oblanceolate, alternate, adaxial surface darker than the abaxial, with short petiole and midrib visible on basal half of leaf adaxially and two-thirds of the leaf from the base abaxially, 2–13 × 0.7–2.2 mm, apex obtuse; involucral leaves green, 4–6, narrowly oblanceolate, 12–20 × 2–5 mm. Inflorescence capitulum with 1–5 buds opening one at a time. Flowers 12–15 mm wide; sepals dark green near apex, translucent margins, 2, unequal laterally with one overlapping the other, ovate-triangular, 5–7 × 3–5 mm; apex acute, gently keeled; petals yellow, usually 5, obovate, 5–9 × 4–5 mm; apex emarginate or bilobed, or cucullate apiculate; anthers yellow, 13–16, ovoid, 0.4–0.6 × 0.3–0.5 mm; filaments yellow, 13–16, filiform, 3–4 mm; style yellow, ± 3 mm long, with ± 5 stigmatic branches, 1.7–3.0 mm long; ovary green, ellipsoid, ± 8 × 4 mm. Fruit capsule green at first, beige at dehiscence, ellipsoid, (4–)7–9 × 3–4(–6) mm; lid with small protuberance apically; sepals persistent on mature fruit. Seeds black, opaque, many, cochleate, ± 0.9 mm wide; testa cells isodiametric; antclinal walls undulate with a U-type pattern sometimes having bi- and tri-furcated apices; undulations long in one plane and short in opposite plane; periclinal walls have a convex relief with a few low-relief domes, and minute papillae covering the cell surface.

Diagnostic characters ( Table 1):— The first noticeable character distinguishing Portulaca trianthemoides from its closest resembling Portulaca species, P. oleracea , is its growth habit. The latter species has a prostrate habit while that of the former is consistently erect to sub-erect ( Fig. 4A, B ). Although a thin main taproot ( Fig. 4C ) is common to the two species, leaf shape is another consistent difference. Portulaca oleracea has broadly obovate-spathulate leaves while those of P. trianthemoides are narrowly oblanceolate ( Fig. 4D ). Sepals (2) are keeled in both species near the apex ( Fig. 4E, F ), but those of P. trianthemoides appear to be uneven laterally ( Fig. 4G ), with one overlapping the other in bud ( Fig. 4E ) and the keel is gentle near the apex, while sepals of P. oleracea are strongly keeled. Both species have persisting sepals ( Fig. 4H ) and yellow flowers; however, the flowers of P. oleracea are relatively inconspicuous relative to leaf size and much smaller (2–6 mm wide) than those of P. trianthemoides (12–15 mm wide; Fig. 4I ). Anther number also differs between the two species where P. oleracea has an average of about 5 while P. trianthemoides has about 13–16 ( Table 1). Lastly, while the operculum ( Fig. 4J ) of both species have an apical protuberance, the surface of seed testa cells ( Fig. 4K ) of P. trianthemoides does not appear to match any of the known morphotypes/subspecies of P. oleracea ( Danin et al. 2008, Ocampo 2015, Danin et al. 2016, Rad et al. 2017). Seed testa cell micromorphology seems to be unique in P. trianthemoides in that the U-type undulations of anticlinal walls are long in one plane of the cell surface and short in the other, while periclinal walls have a convex relief with a few scattered low-relief domes, and minute papillae covering the cell surface. However, since seed testa cell micromorphology also varies among the morphotypes/subspecies of P. oleracea ( Danin et al. 2008, Ocampo 2015, Danin et al. 2016, Rad et al. 2017), the macromorphological differences outlined above between the two species seem more reliable as diagnostic characters. It is also worth noting that morphotypes/subspecies of P. oleracea are very similar macromorphologically ( Danin et al. 1978), with differences seen largely at the micromorphological level (of seed testa cells) rather than on a macromorphological level, which is not the case when comparing P. trianthemoides with P. oleracea .

Ecology:— Portulaca trianthemoides grows on open spaces, featuring scattered trees [e.g., Dichrostachys cinerea (L.) Wight & Arn. and Vachellia Wight & Arn. spp. ), grasses (mostly Tragus berteronianus Schult. ), and various other plant species ( Fig. 5 ) including Trianthema salsoloides Fenzl ex Oliv var. transvaalensis (Schinz) Adamson (1962: 248) , which, when observed from a distance, can be mistaken for P. trianthemoides due to their similar appearance. This resemblance is reflected in the specific epithet ‘ trianthemoides ’, which means “similar to” or “resembling” Trianthema Linnaeus (1753: 223) ].

Portulaca trianthemoides is an endemic species in the Soutpansberg region, representing one of two Portulaca species exclusively found in Limpopo. A further Portulaca species, P. waterbergensis , appears to be confined to the Waterberg region ( Peckover 2021), which is however distinct from the Soutpansberg. This smaller species thrives on rocky outcrops in shallow soil (personal observation).

It is important to note that the Soutpansberg area was recognised by Hahn (2002) as a hotspot for plant endemism, including around 22 endemic species out of the approximately 2443 plant species recorded ( Hahn 2019). Now, with the rediscovery of P. trianthemoides , it can rightfully join the list of species endemic to this region.

Despite the apparent existence of only one population of Portulaca trianthemoides , the high number of individuals (>15,000) within that population suggests that, based on Criterion D (very small or restricted population, where a species is deemed vulnerable if there are less than 1000 mature individuals) of the International Union for Conservation of Nature ( IUCN 2022), the species should have a conservation status of “Least Concern” (LC).

Portulaca trianthemoides appears to be summer-flowering. Like other Portulaca species, flowers of the species seem to open wide on sunny days, but open partially or remain closed when overcast. Matthews & Levins (1985) also reported that flowers of Portulaca species in south-eastern United States open on sunny days, with flowers lasting a day and may be self-pollinated even when they do not open. P. trianthemoides flowers tend to start opening at c. 9H00, are fully opened at c. 10H00, and close around 11H00; however, closing can occur earlier on overcast days or flowers may not open at all. This is similar to some other species of Portulaca e.g., P. oleracea is reported to flower ‘in the morning’ ( Phillips 2002); however, other species like P. waterbergensis only have open flowers towards the afternoon ( Peckover 2021). According to Geesink (1969), Portulaca species seem to be mostly self-pollinated; however, some studies suggest that pollination may be achieved by bees in certain species (Pinto & Schlindwein 2014). However, more studies to document visitors and pollinators are needed.

Portulaca trianthemoides plants appeared to have been eaten by species of Cletus Stål (1860: 236) (Horned Coreid Bugs of the family Coreidae ), which were seen on a few occasions at the site of holes, or damaged parts, of leaves. Species of Cletus , such as C. punctiger Dallas (1852: 494) , are known to be herbivorous pests to sorghum and other grasses in India ( Kalaisekar et al. 2017).

It is worth noting that there were two other species of Portulaca ( P. oleracea and P. hereroensis ) co-occurring with P. trianthemoides ; however, no hybrids or intermediates were observed or previously described. It is common to find co-occurring Portulaca species in southern Africa e.g. P. kermesina N.E. Brown (1909: 91) and P. quadrifida grow together in Postmasburg (Northern Cape), and P. kermesina , P. oleracea , and P. hereroensis grow in the same vicinity in Polokwane (Limpopo) [personal observation].

Portulaca trianthemoides plants and soil were collected from the habitat for growing the plants in Durban for further investigations; however, the plants did not survive for more than a couple months irrespective when grown in habitat soil, river sand (gravel), or potting soil. These plants seemed to struggle even when grown in the same conditions as other Portulaca species including P. oleracea . This may strengthen the suggestion that the species is habitat-specific and may also be another indication that it is not synonymous with its most closely resembling species, P. oleracea , which has a cosmopolitan distribution ( Wild 1961, Phillips 2002).

Specimens examined:— SOUTH AFRICA. Limpopo province, 2229CD, Zoutpansberg, Soutpan (west side of -), 20 January 1931, C. E. B. Bremekamp & H. G. W. J. Schweickherdt 231 (isolectotype, PRE!) ; 2229CD, Zoutpansberg, Zoutpan , western side, 21 January 1931, C. E. B. Bremekamp & H. G. W. J. Schweickherdt 231 (lectotype, PRE!) ; 2229CD, Zoutpansberg TVL, 12 April 1934, H. G. W. J. Schweickerdt & I. C. Verdoorn 458 ( K image!) ; 2229CD, Bergpan Saltworks, Farm Soutpan, Soutpansberg , 18 December 2022, W. R. Woodenberg et al. 16 ( NH!) ; 2229CD, Bergpan Saltworks, Farm Zoutpan, Soutpansberg , 23 February 2023, W. R. Woodenberg et al. 25 ( NH!) .

Figures

FIGURE 3. Image of the proposed lectotype specimen of Portulaca trianthemoides collected by Bremekamp and Schweickerdt 231 (10107, PRE) on 21 January 1931. © South African National Biodiversity Institute (SANBI). Reproduced with the consent of SANBI.

FIGURE 4. Portulaca trianthemoides showing A. erect to B. sub-erect growth form; C. thin taproot; D. narrowly obovate leaf; E. uneven pair of sepals (arrows), one enveloping the other; F. the keel present toward the apex of the sepal; G. sepals showing one wider than the other (uneven); H. persisting sepals surrounding central capsule flanked by two empty lower halves of spent capsules; I. a flower with yellow petals; J. lid of capsule with apical protuberance; K. seed testa cells showing long (L) and short (S) undulations on opposite planes of epidermal cells, and low-relief domes (*). Scale bar = 10 mm (A, B), 1 mm (C, G–I), 5 mm (D–F, J), 20 µm (K). Images by R. Nemando (A, D–F), W.R. Woodenberg (B, C, G–J), and S. Naidu (K).

FIGURE 5. A. Habitat of main subpopulation c. 1 km south-east of saltpan; B. numerous small plants including Portulaca trianthemoides are scattered in the sandy, open patches of the landscape; and C. darker humus-rich soil beneath the sandy surface. Images by R. Nemando (A, C) and W.R. Woodenberg (B).