Pseudohydrosme ebo Cheek, Tchiengué, and van der Burgt 2021
- Taxonomic revision of the threatened African genus Pseudohydrosme Engl. (Araceae), with P. ebo, a new, critically endangered species from Ebo, Cameroon
- Published in
- Cheek, Martin, Tchiengué, Barthélemy, van der Burgt, Xander (2021): Taxonomic revision of the threatened African genus Pseudohydrosme Engl. (Araceae), with P. ebo, a new, critically endangered species from Ebo, Cameroon. PeerJ 9: 1-32, DOI: 10.7717/peerj.10689, URL: http://dx.doi.org/10.7717/peerj.10689
- Pseudohydrosme ebo
Phenology: flowering in September and early October; leaves early December; fruiting unknown.
Conservation: Pseudohydrosme ebo is known from only one location, with three sites along a section of valley 1.3 km long and only 50 – 100 mature individuals in total have been seen by the collectors (second and third authors). These sites are along former logging roads which have reverted to forest (X. Van der Burgt, 2019, personal observation) as well as intact forest. In the fourteen years since 2006, botanical surveys have been made almost annually, at different seasons, over many parts of the formerly proposed National Park of Ebo. About 3000 botanical herbarium specimens have been collected, but despite the species being so spectacular in flower, with individual inflorescences lasting potentially two weeks (if they prove to be similar in phenology to those of P. gabunensis), this species has been seen nowhere else in the c. 2000 km 2 of the Ebo Forest. However, much of this area has not been surveyed during the flowering season of the species, or not surveyed at all for plants. While it is likely that the species will be found at additional sites, there is no doubt that it is genuinely range restricted. Botanical surveys for conservation management in forest areas neighbouring Ebo resulting in thousands of specimens being collected and identified have failed to find any specimens of Pseudohydrosme (Cheek et al., 1996; Cable & Cheek, 1998; Cheek, Onana & Pollard, 2000; Harvey et al., 2004; Cheek et al., 2004; Cheek, Harvey & Onana, 2010; Harvey, Tchiengue & Cheek, 2010). It is possible that the species is unique to Ebo and truly localised. The area of occupation of Pseudohydrosme ebo is estimated as 4 km 2 using the IUCN preferred cell-size. The extent of occurrence is the same area. In February 2020 it was discovered that moves were in place to convert the forest into two logging concessions (e. g. https: // www. globalwildlife. org / blog / ebo-forest-a-stronghold-for-cameroons-wildlife / and https: // blog. resourceshark. com / cameroon-approves-logging-concession-that-will-destroy-ebo-forest-gorilla-habitat / both accessed 19 September 2020). This would result in logging tracks that would allow access throughout the forest allowing poachers of rare collectable plants such as Pseudohydrosme, and timber extraction would open up the canopy and remove the intact habitat in which Pseudohydrosme grows. Additionally, slash and burn agriculture often follows logging trails and would negatively impact the populations of this species. Fortunately the logging concession was suspended due to representations to the President of Cameroon on the global importance of the biodiversity of Ebo (https: // www. businesswire. com / news / home / 20200817005135 / en / Relief-in-the-Forest-Cameroonian-Government-Backtracks-on-the-Ebo-Forest accessed 19 September 2020). However, the forest habitat of this species remains unprotected and threats of logging and conversion of the habitat to plantations remain. Pseudohydrosme ebo is therefore here assessed, on the basis of the range size given and threats stated as CR B 1 + 2 ab (iii), that is Critically Endangered.
Figs. 1 – 3, 6 and 7.
Terrestrial herb, to 1.55 m tall. Rhizome cylindric, c. 3 cm diam. obliquely erect to almost parallel to substrate surface, only upper part exposed, surface with transverse ridges (leaf scars) about 2 mm deep, 2 mm apart. Roots adventitious, thick, fleshy, c. 5 mm diam., scattered along length of rhizome, asexual reproduction not detected. Leaf to 1.55 m tall, petiole terete, to 2 cm. diameter at base, green, inconspicuously spotted yellow, mature plants with minute, patent, extremely sparse prickles 0.5 mm long. Blade of youngest seedlings sagittate-elliptic, 5 × 2.5 cm, apex obtuse, basal sinus 1.5 × 1.5 cm, petiole 6 – 7 cm long. Older seedlings, in successive years with leaves developing first slits and then divisions, becoming triangular in outline with a broad basal sinus. Blade of mature leaves dracontoid, primary division 35 – 40 × 38 – 43 cm, pinnatisect, lobes 5 – 8, dimorphic, larger, mainly distal lobes oblong 12.5 – 22 × 3.8 – 6.5 cm, apex acuminate or truncate-bifid (biacuminate), acumen 0.8 – 1.5 cm long, smaller, mainly proximal lobes ovate c. 8 × 3.5 cm; lateral veins 6 – 11 conspicuous on abaxial surface, on each side of the midrib, uniting to form a regular looping submarginal vein 3 – 6 mm from the margin, higher order veins reticulate. Inflorescence: Cataphylls 4, phyllotaxy spiral, light brown, with light green spots, membranous, successively increasing in size from proximal to distal, the outermost triangular-broadly ovate, amplexicaul 3 × 4 cm, the third in succession narrowly lanceolate-oblong, 12 × 2 cm, the fourth 18 – 19 × 1.5 – 4 cm; peduncle 3.5 – 4.5 × 0.6 – 0.7 cm, with minute, patent, extremely sparse prickles 0.5 mm long, colour as petiole. Spathe 24 – 30 (– 34.5) × 8 cm long basal 1 / 2 – 3 / 4 subcylindric, convolute, funnel-shaped, 1.8 – 4 cm wide at 2 cm above the peduncle, 6 – 8 cm wide at 8 cm above the peduncle, and 8 – 9 cm wide at 15 cm above the peduncle, the distal part (limb), half to one third of the total spathe length, flaring widely and curving forward, hood-like, shielding the spadix, the apex with a triangular acumen 3 – 4 × 1 cm; outer surface of both tube and limb dull white, with pale brown-red ribs running longitudinally along veins from base of tube to mouth of limb; inner surface of spathe light reddish brown, with wide pale green veins, gradually becoming slightly darker along the midline; mouth facing horizontally, transversely elliptic, 8 – 10 cm high, 20 – 25 cm wide, margin entire. Spadix sessile, cylindrical, 50 – 85 mm long, 10 – 18 mm diam. Female zone 24 mm long, 15 – 18 mm wide, female flowers sparsely scattered, c. 30, laxly arranged, covering only about half the surface of the spadix axis, the axis visible between the flowers, sometimes not contiguous with the male zone, the axis then naked for up to 10 mm. Male zone 37 – 55 mm long, 10 – 14 mm wide, apex rounded, completely covered in densely arranged male flowers, sterile appendix absent. Male flowers with 2 – 5 stamens, sometimes paired or in groups of 3 – 5, stamens free, sessile, prismatic, 5 mm long, isodiametric in plan-view, 5 – 6 faceted, (1.5 –) 2 mm diam., apex convex, minutely papillate; anther thecae lateral, tetrasporangiate (Fig. 6 F), oblong-elliptic, running the length of the stamen, with apical pore (Fig. 6 E). Female flowers with ovary globose, 4 mm diam., 3 - locular (Fig. 6 I), very rarely 2 - locular, style 1 – 1.5 mm long, 1 mm diam., stigma pale yellow, 0.5 mm thick, 2 – 2.25 mm wide, strongly 3 - lobed (Fig. 7 E), lobes with a narrow midline groove, apex rounded. Berry and seed not seen.
Notes: Pseudohydrosme ebo came to the attention of the first author in late Aug. 2018 on seeing van der Burgt 1888, collected in 2015. Plans were made to revisit the collection site at the next available opportunity, in December 2019, when leaves were found by the third author (van der Burgt 2377), but unfortunately fruits were not found. At the same time a second site was discovered 1.3 km distant from the site found in 2015. In February 2020 van der Burgt found at Kew an overlooked, additional specimen, Morgan 25, which is the earliest known record of the species, dating from 2010, and since it has multiple duplicates, has been selected as type of the new species. The associated collection data previously mislaid was rediscovered in May 2020. Alvarez with van der Burgt, and Ngansop, discovered in December 2019 seedlings of the new species, at three different stages, preserved as Van der Burgt 2377 sheet 1 / 4 (see Fig 7). Clearly the species at this site is reproducing itself. Associated photographs also show plants of different ages. Abwe & Morgan (2008) and Cheek et al. (2018 b) characterise the Ebo forest, and give overviews of habitats, species and importance for conservation. Fifty-two globally threatened plant species are currently listed from Ebo on the IUCN Red List website and the number is set to rise rapidly. The discovery of a new species to science at the Ebo forest is not unusual. Since numerous new species have been published from Ebo in recent years. Examples of other species that, like Pseudohydrosme ebo appear to be strictly endemic to Ebo on current evidence are: Ardisia ebo Cheek (Cheek & Xanthos, 2012), Crateranthus cameroonensis Cheek and Prance (Prance & Jongkind, 2015), Gilbertiodendron ebo Burgt and Mackinder (Van der Burgt et al., 2015), Inversodicraea ebo Cheek (Cheek et al., 2017), Kupeantha ebo M. Alvarez and Cheek (Cheek et al., 2018 a), Palisota ebo Cheek (Cheek et al., 2018 b). Further species described from Ebo have also been found further west, in the Cameroon Highlands, particularly at Mt Kupe and the Bakossi Mts (Cheek et al., 2004). Examples are Myrianthus fosi Cheek (Cheek & Osborne, 2010), Salacia nigra Cheek (Gosline, Cheek & Kami, 2014), Talbotiella ebo Mackinder and Wieringa (Mackinder, Wieringa & Van der Burgt, 2010) Additionally, several species formerly thought endemic to Mt Kupe have subsequently been found at Ebo, for example Coffea montekupensis Stoff. (Stoffelen et al., 1997), Costus kupensis Maas and H. Maas (Van de Kamer et al., 2016), Microcos magnifica Cheek (Cheek, 2017), and Uvariopsis submontana Kenfack, Gosline and Gereau (Kenfack et al., 2003). Therefore, it is possible that Pseudohydrosme ebo might yet also be found in the Cameroon highlands, for example at Mt Kupe, further extending westward the known range of the genus. However, this is thought to be only a relatively small possibility given the spectacular nature of this plant, and the high level of survey effort at for example Mt Kupe: if it occurred there it is highly likely that it would have been recorded already. Additional characters separating Pseudohydrosme ebo from P. gabunensis are show in Table 1. It is to be hoped that further studies of live plants of P. ebo will be possible to determine if, like P. gabunensis it also reproduces asexually from the root tips. The biogeography of the Cameroonian Pseudohydrosme ebo is very different from that of the two Gabonese species of the genus growing c. 450 km to the South. The Gabonese species grow on recently deposited, sandy coastal soils. Although the Gabonese species also experience a wet season of about 3 m of rainfall per annum, it is differently distributed: the dry season in Libreville occurs from June to September inclusive and is colder than the wet season. In contrast at Ebo the geology at the Pseudohydrosme location is ancient, highly weathered basement complex, with some ferralitic areas in foothill areas which are inland, c. 100 km from the coast. The wet season (successive months with cumulative rainfall> 100 mm) is almost the inverse of at Libreville, falling between March and November and is colder than the dry season (Abwe & Morgan, 2008). In addition, the affinities of Ebo as indicated by shared plant species, seems to be with other parts of the Cross-Sanaga biogeographic area, the Cameroon Highlands, rather than with Gabon (see above).
Distribution and ecology: Cameroon, Littoral Region, known only from three sites at one location in the Ebo forest near Yabassi-Yingui, in late secondary and intact, undisturbed lowland evergreen forest on ancient basement complex geology, rainfall c. 3 m p. a., drier season October-March; 300 – 400 m alt.
Etymology: named as a noun in apposition for the forest of Ebo, in Cameroon’ s Littoral Region, Yabassi-Yingui Prefecture, to which this spectacular species is globally restricted on current evidence.
Additional specimens: Cameroon, Littoral Region, Ebo proposed National Park, fl. 8 Oct. 2015 van der Burgt 1888 (K! YA!); ibid., st. (leaves) 9 Dec. 2019, van der Burgt 2377 (K!, MO!, P!, WAG!, YA!).
Differing from Pseudohydrosme gabunensis Engl. in the ovaries 3 - locular, the stigma conspicuously 3 - lobed, very rarely 2 - locular / lobed (vs. usually 2 - locular, 2 - lobed, rarely 3 - locular / lobed), the female zone of the spadix only sparsely covered in flowers, the spadix axis visible between the flowers (vs. completely covered in flowers), the spathe at anthesis 24 – 30 (– 34.5) cm long, the outer surface dull white with longitudinal brown stripes, inner surface light reddish brown with wide pale green veins (vs. (30 –) 40 – 55 (- 70) cm long, uniformly white, green or yellow on both surfaces, inner surface bicoloured, the mid-limb area dark purple, sharply demarcated from the marginal white / yellow coloured area).
Type: B. J. Morgan 25 (holotype K!; isotypes B! MO! YA!), Cameroon, Littoral Region, Yabassi-Yingui, Ebo proposed National Park, fl. September 2010.
Local names and uses: none are known.