Impatiens ×troupinii Eb.Fisch., Abrah., Holstein

Fischer, Eberhard, Abrahamczyk, Stefan, Holstein, Norbert & Janssens, Steven B., 2021, Evolution of Impatiens (Balsaminaceae) in the Albertine Rift - The endemic Impatiens purpureoviolacea complex consists of ten species, TAXON 70 (6), pp. 1273-1299 : 1293-1294

Impatiens ×troupinii Eb.Fisch., Abrah., Holstein & S.B. Janssens, nothosp. nov.

– Holotype: Rwanda. Western Province, near Uwinka, km 94 road Butare–Cyangugu, c. 2450 m, Mar 1980, Bridson 470 ( BR barcode BR 0000008693433!; isotype: K!).

Diagnosis. – This natural hybrid is intermediate between its parents, Impatiens purpureoviolacea and I. gesneroidea . It differs from I. gesneroidea in the hairy ovary, the dark magenta dorsal petal and lateral united petals, and the spur that is ± abruptly constricted and strongly coiled. It differs from I. purpureoviolacea in the dark magenta flowers with green spur, the hairy spur and dorsal petal, and the shape of the lateral united petals.

Description. – Plants erect or ascending, stems 50–150 cm long. Leaves either resembling those of I. gesneroidea or those of I. purpureoviolacea , petiole (5) 8–35 (48) mm long, with 1–3 (4) extrafloral nectaries, lamina 27–87 (102) × 26–50 mm, margin with 5–9 (10) pairs of extrafloral nectaries. Inflorescence with 1–2 flowers, peduncle 10–15 mm long, pedicel 18–23 mm long. Flowers magenta, lower sepal entirely greenish, petal base barely yellow, purple maculae at base small sometimes deeply hidden in the throat. Lateral sepals (3) 4.5–5.5 (8) × 2 mm, lanceolate, green. Lower sepal deeply navicular, 10–12 mm long, 6–7 mm deep, ± abruptly constricted into a spiraled, broadly filiform spur, 2 mm in diameter, spur (14) 18–21 mm long. Dorsal petal helmet-like, dark magenta, with green crest above ending in a long spur, not or only slightly bilobed, 9–11 × 10–12 (14) mm. Lateral united petals dark magenta, with dark red and yellow spots at throat, 14–18 mm long, upper lateral petal 9–10 × 4.5–8 mm, lower lateral petal 14–17 × 6–9 mm. Ovary pubescent, 4–5 mm long. Fruit 12–14 × 5–6 mm. Figures 5C,D, 16.

Ecology. – Montane rainforest, 2250–2450 m, between the parents.

Distribution. – Rwanda, Nyungwe National Park.

Etymology. – Named after Georges M.D.J. Troupin (1923– 1997), the author of Flore du Rwanda, who first discovered the hybrid together with D. Bridson.

Specimens examined. – Rwanda. Western Province, Nyungwe National Park, near source of Rukarara , 2250 m, E. Fischer 13912 ( BONN, KOBL) .

Notes. – This new hydrid was already mentioned by Troupin & Grey-Wilson (1983) as occurring in clearings of montane forest near Uwinka at 2400 m. It has been observed there by the first author in 1985, vegetatively more resembling Impatiens purpureoviolacea but with clearly intermediate flowers. Grey-Wilson (1989) described this new hybrid, hitherto only known from one locality in Rwanda (Uwinka) and he stated that “there is little doubt […] that the parents are I. gesneroidea var. gesneroidea and I. purpureoviolacea ” ( Grey-Wilson, 1989: 717) . However, he did not name it formally. In 2017, the hybrid was again collected at the type locality of I. purpureoviolacea growing as a single individual and apparently not as hybrid swarm between its parents I. purpureoviolacea and I. gesneroidea . It has been observed only as a rare plant in single individuals.