AMORPHOPHALLUS DUMBOI
PROTOLOGUE: Amorphophallus dumboi Eb.Fisch., B.Dumbo & L.Dumbo, published in Fischer E, Dumbo B, Dumbo L (2022) A new species of Amorphophallus (Araceae) from Eastern D.R. Congo, and a new record of the genus from Rwanda. Plant Ecology and Evolution 155(3): 333-342..
Amorphophallus dumboi Eb.Fisch., B.Dumbo & L.Dumbo, sp. nov.
Type. D.R. CONGO – Lacs Edouard et Kivu • S Kivu, Kahuzi-Biéga National Park, transitional rainforest at Mulolo, partially submerged along small stream; 2°29’06.42”S, 28°21’22.09”E; 1108 m; Dec. 2018; B. Dumbo & L. Dumbo s.n.; holotype: BR [BR0000015253569V].
DISTRIBUTION: DE Congo: DR Congo.
DISTRIBUTION NOTE: Only known from the rainforests in the southern part of Kahuzi-Biéga National Park, Eastern Democratic Republic of the Congo.
SPECIES DESCRIPTION:
Tuber irregular-globose to ovoid, 6–8 × 2.5–5.5 cm. Leaf with 3 pinnae, each 1-pinnate to 1-pinnatifid. Petiole 70–75 cm long. Lamina diameter up to 120 cm. Rachis of each pinna 35–37 (48) cm long, winged. Terminal leaflet up to 16.5 cm long and 4.5 cm wide, with long acumen of 2.5 cm length. Cataphylls 3, the inner one ca 9–10 × 1.5–2 cm, the outer ones much shorter, dark with darker veins.
INFLORESCENCE:
Inflorescence up to 125 cm tall, erect, appearing simultaneously on the same bulb with the leaf, smell very unpleasant. Peduncle smooth, 90–98(–105) cm × 1.5 cm, with small roundish spots. Spathe 18–25.5 (30) cm long, cylindrical, without a constriction, tube 11–12(–15) × 5.8–6.2 cm, interior (adaxial) side basally with irregular rounded to elongate smallpox-like projections of 0.2–1 mm length, between and on the veins, open limb erect, rim-shaped to elongate-triangular 15–16 × 6–8 cm, purple, margin entire. Spadix sessile, 25.5–32.5(–38) cm long, slightly longer than spathe, carpellate zone cylindrical, 2.5–5.2 × 2.5–2.8 cm, flowers mostly congested, staminate zone cylindrical, 4.8–5.3 ×2.5–2.8, flowers dense, appendix conical, 16–18 × 3.8–5 cm, smooth and velvet-like, basally with longitudinal furrows, staminodes absent, without a sterile zone between the carpellate and staminate zone. Carpellate flowers 4–4.6 mm long, ovaries elongate-ovoid, 3.5–4 ×3–4 mm, unilocular, style slender, 1–1.2 mm long, same colour as ovary, stigma 1.2–1.3 mm in diameter, usually unlobed and head-shaped. Staminate flowers 1–1.5 × 1.3–2.24 mm, with 3–4 stamens; anthers free, globose to cubic with rounded edges, filaments only 0.1–0.3 mm long, free or sometimes basally connate but not forming a columna, pores circular, one apical pore per theca. Infructescence unknown. Observed in flower from August to April.
ECOLOGY:
Transitional montane rainforest at Mulolo, partially submerged along small stream, 1108 m, together with numerous ferns and Impatiens species.
DISTRIBUTION MAPS:
ETYMOLOGY:
Named after Dumbo Kilundo (1 January 1930−18 September 2020), one of the most knowledgeable botanists from D.R. Congo, despite that he never received formal training. Born in Kisanga (Mulolo), Shabunda, he went to the Institut de Recherche Scientifique en Afrique Centrale (IRSAC) at Lwiro, today Centre de Recherche en Sciences Naturelles (CRSN). There he worked first with A.R. Christiaensen and later with G. Troupin. He made major contributions to the knowledge of the Flora of Central Africa, first for the IRSAC, later as Head of Irangi Forest Reserve and for the Herbarium of Lwiro.
NOTES:
1. Amorphophallus dumboi differs from Amorphophallus margretae in the leaves and inflorescences that appear at the same time on the same tuber (leaves appear after inflorescence in Amorphophallus margretae), the peduncle about 4 times the length of the spathe (peduncle not exceeding 2 times the length of the spathe in Amorphophallus margretae), and the inner base of spathe with irregular rounded to elongate smallpox-like projections of 0.2–1 mm in length, between and on the veins (inner base of spathe smooth, with shallowly elevated dark veins in Amorphophallus margretae).
2. Preliminary IUCN conservation assessment. Critically Endangered: CR B2ab(iii). Amorphophallus dumboi is only known from the type locality. The estimated AOO is 4 km² (assuming a 4 km² grid cell size). The habitat, a submontane rainforest, is under potential threat of illegal logging but is actually protected as part of Kahuzi-Biéga National Park.
3. Amorphophallus dumboi is one of the few species in the genus recorded from the Albertine Rift in Eastern D.R. Congo. The only other species known from that area is Amorphophallus margretae, which has been recorded only from the type locality in the former Irangi Forest Reserve. The first author could collect a specimen from this area in 1991, and study the vegetation (Fischer 1996). Amorphophallus margretae occurs on the forest floor in a Gilbertiodendron dewevrei-Cynometra alexandri rainforest near a stream and grows also in the water of a stream according to the collector of the type specimen A.R. Christiaensen (“forêt ombrophile dans l’eau de la rivière”). Observations in the field and in cultivation at the Botanical Gardens of the University of Bonn revealed that it has, like most other species, a pronounced dormancy, confirmed also by A.R. Christiaensen (“herbe en fleurs, feuille absente”). The leaves appear after flowering and are only visible in March to April or October to December. Unfortunately, the individual in cultivation did not survive, and was also not documented as a voucher. Moreover, the forest at the type locality has now been logged. Thus, Amorphophallus margretae is considered as Critically Endangered (CR), possibly extinct. Amorphophallus dumboi grows in an inundated rainforest close to a stream. Observations at the type locality showed that it has no dormancy, and that inflorescences and leaves are present at the same time on one single tuber. The population of Amorphophallus dumboi has been visited four times and there have always been inflorescences and developed leaves on one single bulb. In the only known specimen of Amorphophallus margretae only the inflorescence with bulb is present indicating a marked dormancy. This is confirmed by a personal observation of the first author at the type locality at Irangi who recorded only leaves without inflorescences. Ittenbach (2003) showed that the basal inner (adaxial) side of the spathe is of special diagnostic value. He could distinguish 12 types of sculpture from verrucate or covered with hairy emergences to elevated veins or parallel ribs. Amorphophallus gallaensis and Amorphophallus margretae have typical elevated veins that are usually dark. Amorphophallus dumboi has a unique kind of sculpture at the basal inner side that has not been described by Ittenbach (2003). It consists of irregularly rounded to elongate smallpox-like projections that have the same colour as the surrounding spathe interior. They are arranged longitudinally along and between the veins
REFERENCES:
1. Plants of the World Online, Royal Botanic Gardens, Kew — Amorphophallus dumboi Eb.Fisch., B.Dumbo & L.Dumbo