Palisota alboanthera Burg & E. Bidault, 2019

Bidault, Ehoarn & Burg, Willem Joost van der, 2019, Novitates Gabonenses 90: Palisota (Commelinaceae) revisited: description of eight new species from Central Africa and notes on the identity of P. satabiei and P. bogneri, Candollea 74 (2), pp. 169-202 : 180-183

2. Palisota alboanthera Burg & E. Bidault , spec. nova ( Fig. 2D–G , 4 ).

Holotypus: GABON. Prov. Ngounié: Mabounié , Transect TS13 , 00°46'39"S 10°33'57"E, 89 m, 13.XI.2013, fl., Stévart et al. 4780 ( BRLU!; isotype: BR!, LBV!, MO!, P!, WAG!).

Palisota alboanthera Burg & E. Bidault most closely resembles P. bogneri Brenan but differs by its overall more robust habit, purple to violet flowers, and unequal anthers, the upper two yellow, the lower one white or pale yellow.

Stemless rosette herb to 20–50 cm tall, with ± 10 leaves, in small gregarious subpopulations forming patches of individuals of various sizes; fibrous roots partially swollen at the apex, otherwise narrowly fusiform. Leaves in a pseudo-whorl; sheath ± 2–5 cm long, forming an acute angle with the pseudopetiole; pseudopetiole variable in length, up to 28 cm, canaliculate; lamina narrowly obovate, 14–27(–45) × 3–10(–15) cm, base long-decurrent to cuneate, margins entire, apex acuminate, glabrous on both surfaces except for small appressed gingercolored trichomes on the margins, upper surface green to shiny dark green, lower surface with whitish primary venation. Inflorescences axillary, borne at the base of the plant, decumbent and erect at the apex, up to ± 10 cm, 8.5–24 cm long, unbranched; peduncle 7–14 cm long, 4–5 mm in diam., glabrous, pink to violet, with 3(–4) persistent leafy ovate acute bracts of the same color, 1–3 × 0.5–2 cm; thyrse dense, globose, 1.5–2.5 cm in diam., to oblong, 4–10 × 1.5–2.5 cm; cincinni 3–5 mm long, elongating to ± 1.5 cm at maturity, erect, each bearing ± 6 flowers. Flowers either all male, functionally male, or functionally female on the same inflorescence, bud pale pink to dark purple, flower 5–7 mm in diam., pedicel 6–9 mm long, erect at anthesis, becoming spirally contorted after flowering, perianth reflexed after anthesis, then closing again. Sepals equal, oblong, slightly concave, 3–4 × 1 mm, petaloid, pale pink to violet, glabrous or with a few purple to violet trichomes at the apex on the abaxial surface. Petals similar to sepals, slightly more translucid, glabrous. Staminodes 3, filaments with long, white, apparently beaded, spreading trichomes, antherodes lacking. Stamens 3, unequal, erect, filaments white, the two upper ones with a glabrous filament 2–3 mm long, anthers oblong, slightly curved, 1.5 × 0.8 mm, basifixed, yellow; the lower stamen more robust, filament 3–3.5 mm long, glabrous, anther 1.5 × 1.2 mm, dorsifixed, white, occasionally pale yellow, pollen sacs curved, reniform, pollen same color as the anther, anther indehiscent on functionally female flowers. Ovary ovoid, 1.5 × 0.8 mm, glabrous, white to dark violet, style 3 mm long on the female flower, stylode truncated on the male flower, glabrous, pale pink to violet on the basal two third of its length, pale pink toward the apex, stigma truncate. Fruits not seen.

Etymology. – The species epithet refers to the white anther of the lower stamen in the flowers of this taxon. While white anthers are not uncommon in Palisota , this species is the only one we are aware of that has two yellow anthers and a single white one.

Distribution and ecology. – Palisota alboanthera appears to be endemic to Gabon, where it is known from Moyen-Ogooué, Ngounié, Ogooué-Ivindo and Ogooué-Lolo provinces ( Fig. 5 ). It grows in the understory of mature to secondary forests on terra firme, occasionally on rocky slopes, more often in low areas and close to rivers, but not on inundated ground. It is known from 27 to 840 m elevation.

Conservation status. – The EOO is 16,574 km ², below the threshold for “Vulnerable” status under Criterion B1, and the AOO is estimated at 52 km ², which is below the threshold for “Endangered” status under Criterion B2. Palisota alboanthera is known from 13 collections, all made in the south-central part of Gabon between 1924 and 2017. While the oldest of these, Le Testu 5106, was collected nearly a century ago, we consider that the sub-population it represents is likely to persist today as the area still shows significant forest cover. These 13 collections represent 9 sub-populations. One of these, located at Mabounié, 45 km SE of Lambaréné, is in a mining concession, where exploitation has been planned but is not currently being developed. Two additional collections, representing one sub-population, were made in the Koumounabouali range near Fougamou, where selective logging has been practiced in the past and is still occurring today. Another collection, representing one sub-population, comes from a forestry concession (held by CBG – Compagnie des Bois du Gabon) located 25 km W of Mandji, and we documented yet another sub-population in 2017 in the vicinity of the Louétsi river in Nougnié province, on the site of a planned hydroelectric project, which is expected to lead to its extirpation. The 9 sub-populations represent 9 locations with respect to the most important threat (hydroelectric projects), none of which are located in protected areas. Palisota alboanthera is thus threatened by forestry, mining, and the development of a hydroelectric project, leading to projected decline of its EOO, AOO, the quality of its habitat, number of locations and number of mature individuals. Palisota alboanthera therefore qualifies as “Vulnerable” [VU B1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v)] according to the IUCN Red List Categories and Criteria ( IUCN, 2012).

Notes. – Palisota alboanthera closely resembles P. bogneri by its rosette habit and axillary decumbent inflorescence, but can be distinguished by its more robust habit and pink to purple (vs. white) flowers with three unequal stamen, the lower one becoming white (vs. all stamens yellow). No collections of P. alboanthera have been observed that contain both fruits and flowers, and without floral characters, it can be difficult to distinguish this species from P. bogneri . We believe that Dauby et al. 1688 represents a fruiting collection of P. alboanthera , due to its large size compared to typical P. bogneri , as well as its axillary inflorescence, differentiating it from P. barteri , whose inflorescences are erect and terminal. However, other smallersized plants have been collected that we could not assign with confidence to either P. alboanthera or P. bogneri , such as Wieringa et al. 7374. In the absence of information on the base of the plant, P. alboanthera can be confused with P. akouangoui . Leal et al. 1863, for instance, probably represents P. alboanthera , but is not cited below as a paratype because the absence of the base of the plant precludes identifying it with certainty. Variation in the color of the flowers and the anther of the lower stamen was observed on a recent collection (Bidault et al. 3807), and two individuals from this subpopulation with young and old inflorescences, respectively, were photographed and collected. The young inflorescence bore pink flowers with erect stamens, the lower one being larger and pale yellow, an inflorescence of intermediate age exhibited dark pink (or pale purple) flowers with erect anthers, the lower one being clearly white, whereas the oldest inflorescence had dark purple flowers with reflexed anthers, the lower one being white. This variation could be correlated with floral function: the young inflorescence had functionally male flowers (dehiscence of the lower anther was observed) with a truncated stylode the intermediate-aged inflorescence had functionally male flowers without a style or ovary (although dehiscence of the lower anther was not observed), and the oldest inflorescence comprised functionally female flowers with a fully developed style and deposited pollen, and the dehiscence of the lower anther was not observed. These observations were, however, made at a single time and may not be fully representative of flowering within this species (no living plants have been cultivated). More detailed field observations could reveal functionally bisexual flowers, shown either by maturation of the female features of younger flowers or dehiscence of the anther in the lower stamen of older flowers.

Paratypi. – GABON. Prov. Moyen-Ogooué: Mabounié , à 45 km au SE de Lambaréné, rives de la Ngounié , 00°49'05"S 10°29'12"E, 27 m, 14.X.2012, fl., Bidault et al. 815 ( LBV, MO); ibid. loco, 00°43'04"S 10°36'09"E, 123 m, 17.XI.2013, fl., Bidault et al. 1352 ( BR, BRLU, LBV, MO). Prov. Ngounié: Mabounié , à 45 km au SE de Lambaréné, rte menant au NE de la concession , 00°46'10"S 10°35'50"E, 84 m, 30.X.2014, fl., Bidault et al. 1869 ( BR, BRLU, LBV, MO); Dibwangui, bords de la Louétsi , en remontant vers les rapides , 02°05'49"S 10°35'34"E, 406 m, 17.XI.2017, fl., Bidault et al. 3807 ( BR, BRLU, LBV, MO, P); road from Mandji into CBG concession , 20–25 km W of Mandji, sentier botanique , 01°46'48"S 10°14'12"E, 97 m, 12.XI.2011, fl., Maas et al. 10262 ( WAG); forêt des Echiras , entre Pagha et Luoutèti , 26.XI.1924, fl., Le Testu 5106 ( P); Divinde, 01°02'22"S 11°09'21"E, 419 m, 16.X.2012, fl., Towns & Ongoda 1329 ( WAG); 26.8 km on road Lébamba to Yeno, 02°01'12"S 11°26'30"E, 230 m, 12.XI.1994, fl., Wieringa et al. 3163 ( WAG); 13.5 km on the road Moukabou to Mbigou, 01°40'22"S 11°45'11"E, 840 m, 13.III.2013, y. fr., Wieringa 7397 ( WAG); SW of Fougamou , Koumounabwali massive , 01°18'00"S 10°25'00"E, 250 m, 11.XII.1995, fl., de Wilde et al. 11549 ( LBV, MO, WAG); massif de Koumounabouali , 01°21'42"S 10°26'30"E, 420 m, 9.XII.1996, fl., de Wilde & de Wilde-Bakhuizen 11713 ( LBV, WAG). Prov. Ogooué-Lolo: Mont Iboundji , 01°05'24"S 11°28'48"E, 600 m, 8.II.2000, fl., Sosef et al. 654 ( LBV, WAG).

Figures

Fig. 2. – Palisota akouangoui E. Bidault & Burg (A–C) and P. alboanthera Burg & E. Bidault (D–G). A. Entire plants showing infrutescences; B. Mature fruits, entire and opened, showing seeds; C. Inflorescence showing open flowers, with green lower stamen; D. Living plant with inflorescence; E. Young inflorescence with male flowers, showing erect, pale yellow lower stamen; F. Bisexual flower with reflexed, white lower stamen; G. Detail of swollen roots. [A–B: Bidault et al. 4100; C: Bidault et al. 3785; D–F: Bidault et al. 3807; G: Stévart et al. 4780] [Photos: E. Bidault]

Fig. 4. – Palisota alboanthera Burg & E. Bidault. A. Habit; B. Inflorescence; C. Bisexual flower with reflexed, mature lower stamen; D. Male flower with reduced ovary; E. Sepal; F. Petal; G. Lower stamen; H. One upper stamen; I. Upper staminode; J. One lower staminode; K. Ovary and pistil; L. Staminodial hair; M. Ovary hair. [A: de Wilde & de Wilde-Bakhuizen 11713; B-M: Bidault et al. 1352] [Drawings: H. de Vries]

Fig. 5. – Distribution of Palisota cristalensis E. Bidault & Burg (stars) and P. alboanthera Burg & E. Bidault (triangles). Elevation is represented in levels of grey, and protected areas as shaded.