Commelina dielsii Herter, Revista Sudamer. Bot.

González, Andrés & Hassemer, Gustavo, 2020, Not extinct after all: rediscovery of Commelina dielsii (Commelinaceae) after 140 years, and first record of this species in Uruguay, Phytotaxa 438 (3), pp. 199-206 : 200-204

Commelina dielsii Herter, Revista Sudamer. Bot. 6: 149, f. 11. 1940

≡ Commelina erecta f. dielsii (Herter) Bacigalupo, Hickenia 2: 136. 1995

Type: — ARGENTINA. ENTRE RÍOS: Concepción del Uruguay, Arroyo Duraznillo, unter Gebüsch , 24 January 1878, P. G. Lorentz 1264 (holotype B barcode B100550661 ! [ Figure 1 in Hassemer 2018]; isotypes BAF barcode 00000198!, CORD barcode 00002197!) .

Diagnosis: —absence of reddish trichomes throughout; presence of auricles on the apex of leaf sheaths; spathes with margins fused basally; inflorescences with the upper cincinnus aborted, included in the spathe; flowers with an upper pair of well-developed yellow petals and a lower petal greatly reduced, rather inconspicuous, whitish; anther of lateral stamens yellowish, darker on the borders, lighter in the centre.

Description: —herbs 25–45 cm tall, perennial, terrestrial. Roots thin, fibrous, cream coloured to light yellow, glabrous or minutely pubescent with absorbent hairs. Trichomes on all parts of the plant hyaline to whitish; reddish trichomes absent throughout. Stems decumbent, apex ascending, becoming trailing or straggling, rooting only near the base; internodes 4.5–10.0 cm long, green, minutely pilose. Leaves distichously-alternate, pseudopetiolate, distributed along the stem, pseudopetiole 0.4–0.6 cm; sheaths 1.4–1.9 cm long, pilose, margins setose, with a pair of auricles on the apex, auricles 0.3–0.4 × 0.2–0.3 cm, green, margins ciliate; blades 6.0–8.0 × 1.5–2.0 cm, chartaceous, adaxially dark-green to green, abaxially light-green, drying olive-green on both sides, lanceolate to ovate lanceolate, minutely villous, hairs hyaline, base obtuse to cuneate, margins green to vinaceous, wavy, apex acuminate; midvein conspicuous, impressed adaxially, prominently obtuse abaxially, secondary veins 4–6 pairs, adaxially conspicuous, abaxially inconspicuous. Inflorescences 1–3, terminal or apparently so, peduncles 0.7–1.0 cm, rarely inconspicuous, puberulous with hook-shaped hairs throughout, hairs hyaline; spathes 1.2–2.5 × 0.7–1.5 cm, depressed ovate to subcordate, usually slightly falcate, base connate for 0.6–1.0 cm, cordate to truncate, margin green to vinaceous, minutely pilose along the edge, hairs hyaline, internally light-green, glabrous, veins inconspicuous, externally green, minutely villous, hairs hyaline, veins inconspicuous, becoming conspicuous when dry; upper cincinnus aborted, included in the spathe; lower cincinnus 2–5-flowered, flowers bisexual, peduncle 0.7–1.1 cm long, partially exserted from the spathe, commonly arcuate at post-anthesis, sparsely to densely puberulous. Flowers bisexual, zygomorphic, 3.0– 3.5 cm wide; pedicel 0.7–1.1 mm long, light green, glabrous, reflexed and slightly elongate in fruit; sepals hyaline, whitish to light-greenish, glabrous, persistent in fruit, upper sepal 0.5–0.7 × 0.3–0.4 cm, elliptic, cucullate, apex round, lower sepals 0.7–0.9 × 0.5–0.6 mm, obovate, cucullate, connate, apex round; upper, paired petals 2.0–2.5 × 1.9–2.0 cm, clawed, limb broadly reniform, 1.2–1.5 × 1.9–2.0 cm, yellow, apex rounded, base cordate, claw 0.6–0.8 mm, whitish to yellow, lower petal 0.3–0.5 × 0.1 cm, sessile, whitish; staminodes 3, subequal, filaments 0.7–1.0 cm long, antherodes 6-lobed, 2.0–3.0 × 2.0–4.0 mm, yellow; lateral stamens with filaments gently sigmoid, geniculate distal to the middle, 1.0– 1.5 cm long, white, anthers elliptic to oblong-elliptic, 3.0–5.0 × 1.0–2.0 mm, yellowish, darker on the borders, lighter in the centre, pollen yellowish-orange to cream-orange; central stamen with filament straight or arcuate-decurved, decurved at the apex, 0.7–0.8 cm long, white, anther 5.0–7.0 × 3.0–4.0 mm, sagittate, strongly curved, held near the antherodes, yellow-orange to cream-orange, connective white, pollen yellowish-orange to cream-orange; ovary oblong-ellipsoid, 2.0–3.0 × 1.0–2.0 mm, 5–6-ovulate, glabrous, sparsely papillose, style exceeding the stamens, sigmoid, strongly recurved apically, 1.6–1.9 mm, white, stigma trilobate, white. Capsules 1–2 per spathe, 5.0–6.0 × 3.0–4.0 mm, obovoid, constricted between the seeds, brown, glabrous, sparsely papillose, 3-locular, 2-valved, dorsal locule 1-seeded, indehiscent, ventral locules 2-seeded, dehiscent. Mature seeds not seen.

Photographs of living specimens: — Figure 1 .

Photographs of herbarium specimens: — Figure 1 in Hassemer (2018) (the holotype).

Illustrations: —Figure 11 in Herter (1940).

Etymology: —the specific epithet commemorates the German botanist Friedrich Ludwig Emil Diels (1874–1945), son of the classical scholar Hermann Alexander Diels (1848–1922) and elder brother of the Nobel Prize laureate chemist Otto Diels (1876–1954).

Phenology: —flowering October–March; fruiting December–April.

Distribution: —previously, C. dielsii was only known from the type gathering, which was made in January 1878 around Arroyo Duraznillo, in Concepción del Uruguay, Entre Ríos province, north-eastern Argentina.This population is likely extinct, as no new collection from Argentina was made since then, which is attested by the absence of gatherings of the species (other than the type gathering) among herbaria in Argentina and abroad. The only assuredly extant population of the species is in Paysandú, western Uruguay ( Figure 2 ). Geographic coordinates are not provided here due to conservation concerns. We observed this population in October 2018, and also one year later, in October 2019. The type locality of C. dielsii , in Concepción del Uruguay, Entre Ríos, Argentina, is located ca. 100 km southwards, on the opposite side of the Uruguay River.

Habitat: — Commelina dielsii grows in pampean grasslands on somewhat calcareous sandstone cliffs on the east margin of the Uruguay River ( Figure 3 ), at elevations of 30– 50 m. The species occurs in a rich herbaceous community along with species such as Dyschoriste hygrophiloides (Nees) Kuntze (1891: 486) , Evolvulus glomeratus Nees & C.Mart. in zu Wied-Neuwied (1823: 81–82), Ipomoea bonariensis Hooker (1839 : t. 3665), Manettia cordifolia von Martius (1824: 95–96 , t. 7), Portulaca grandiflora Hooker (1829 : t. 2885) and Sorghastrum pellitum (Hack.) Parodi (1930: 154) , in a very restricted area of ca. 400 m 2.

Conservation status: —Critically Endangered (CR—B2[a,b{iii}]). The species is currently only known from one population, which is outside any environmental protection area. The area where the Uruguayan population of C. dielsii occurs is affected by regular lawn cuts, because this area is included in the Parque Meseta de Artigas, an Uruguayan national historical monument, which is visited by tourists for much of the year. It is urgent that focused conservation efforts be made for C. dielsii , including both in situ and ex situ conservation. According to our observations, the most critical threat to the survival of C. dielsii is the ongoing advance of invasive trees, mainly of the genus Pinus von Linné (1753: 1000) .

Notes: — Commelina dielsii , due to a combination of taxonomically important characters (i.e. absence of reddish trichomes throughout; presence of auricles on the apex of leaf sheaths; spathes with margins fused basally; inflorescences with the upper cincinnus aborted, included in the spathe; flowers with an upper pair of well-developed petals and a lower petal greatly reduced, rather inconspicuous; central stamen with anther sagittate) belongs to the C. erecta von Linné (1753: 41) alliance. The species morphologically most similar to C. dielsii are C. catharinensis , a narrowly endemic species from southern Brazil ( Hassemer et al. 2016) and C. erecta , a widespread species in Africa and the Americas ( Faden 2012, Hassemer 2019).

Commelina dielsii can be distinguished from C. catharinensis by its lateral stamens having the anther lighter in the centre, much darker on the borders (vs. homogeneously yellow in C. catharinensis ) and from C. erecta by its petals being yellow (vs. blue to purple to lilac, rarely pink or white, in C. erecta ). The lateral stamens are taxonomically very important for the classification of Commelina (Hassemer 2019) . Seed characters would likely be useful for distinguishing these three species, but unfortunately we have not been able to study mature seeds of C. dielsii . Furthermore, a satisfactory characterisation of the morphological variation in seeds of C. erecta is still lacking, mainly due to the very wide distribution of this species, and also because its circumscription and delimitation are still unsatisfactory ( Faden 2012, Hassemer 2019). The very application of the name C. erecta is problematic ( Hassemer et al. 2018) and is awaiting a decision of the Nomenclature Committee for the continuation of its use in the current sense.

Commelina dielsii is currently being cultivated in Montevideo ( Uruguay) and in TrÊs Lagoas ( Brazil) by the authors. The species grows well in cultivation, and can be reproduced vegetatively by cuttings, like most Commelinaceae . However, unlike all other species of Commelina that we are cultivating (including C. catharinensis and C. erecta ), cuttings of C. dielsii do not grow roots when kept in water—these cuttings will only grow roots when planted on soil. Cultivated specimens of C. dielsii produce flowers and immature fruits, but so far no mature seeds have been produced, because the developing fruits fail to mature. Pollination experiments on this species and another Commelinaceae species for which the seeds are still unknown— i.e. Tradescantia serrana Hassemer & Funez in Hassemer et al. (2017: 214–223) —are ongoing.

We should remark that, other than the information presented in this work and in Hassemer et al. (2016), almost nothing is known about C. catharinensis and C. dielsii . Therefore, these two species warrant focused multidisciplinary systematic studies, including karyological, anatomical, palynological and molecular phylogenetic investigations. It is especially important that the phylogenetic position of these two species in relation to the widespread, highly variable C. erecta be clarified.

Additional material examined (new record): — URUGUAY. PAYSANDÚ: Meseta de Artigas, 19 October 2019, A. González & L. Ifran s.n. (MVM-23479).

Figures

FIGURE 1. Commelina dielsii in Paysandú, Uruguay. A: overview of a specimen; B: detail of flower.

FIGURE 2. Distribution map of Commelina dielsii (green star).

FIGURE 3. Environment of the population of Commelina dielsii in Paysandú, Uruguay, on the east bank of the Uruguay River. A: view to the north; B: view to the south.