Impatiens galactica Eb.Fisch., Raheliv. & Abrah., 2017

Fischer, Eberhard, Rahelivololona, Marie Elisette & Abrahamczyk, Stefan, 2017, Impatiens galactica (Balsaminaceae), a new spurless species of section Trimorphopetalum from Madagascar, Phytotaxa 298 (3), pp. 269-276 : 270

Impatiens galactica Eb.Fisch., Raheliv. & Abrah. sp. nov. ( Fig. 1 , 2 )

Impatienti messmerae affinis sed habitu minore glabro sine squamibus albis, sepalis lateralibus lanceolatis apice obtuse instructis, sepalo inferiore ovato apice abrupto et ornamentatione aurantiaco instructo, petalo dorsali triangulo dilatato submediano et petalis lateralibus sub formam litterae minore “d” cum parte superiore angusto et petalo superiore angusto apice brevissime instructo valde differt.

Type: — MADAGASCAR. Antsiranana, Parc National Marojejy, small stream near Cascade d´Humbert, S 14°25’58.3’’ E 49°46’22.7’’, E. Fischer 22, 18 October 2014 (holotype TAN!; isotypes P!, B!, MO!, BONN!) .

Decumbent to slightly ascending, perennial herb, up to 35 cm high. Stems reddish brown, succulent, branching and rooting at lower nodes. Plant entirely glabrous. Leaves alternate, spirally arranged, deep green above, pale green below; petioles reddish brown, 7–15 mm and continuously growing. Lamina 35–81 mm × 20–40 mm, leathery, elliptic to lanceolate, apex acute, base shortly attenuate; lateral veins (3)4 or 5 pairs; margin crenate; extrafloral nectaries 1–1.5 mm long, linear, 9 or 10 pairs, at the lamina margin between each pair of teeth, half erect, prominent especially at young leaves. Inflorescence 1- or 2-flowered. Flowers yellowish white, semi-transparent, with an orange-yellow, shiny, 2 mm wide line along the midrib of the lower sepal and a greenish crest on the dorsal petal. Pedicels 30–43 mm long, slender. Lateral sepals 2, 4–5(–6) mm × 1–1.5 mm, lanceolate, acute. Lower sepal (12–) 14–16 mm × (6–) 7–8 mm ovate-lanceolate, shallow naviculate, spurless, tapering to a 1–2 mm long tip. Dorsal petal 14–16 × (6–) 7–8 mm, helmet-like, dorsally conspicuously crested, dilated to a triangle below the middle of the crest, tapering to a 1 long mm tip. Lateral united petals (18–)20–21(–23) mm long, with petals different in size and shape, connivent at the outer tip; upper petal (6–) 7–8 mm × 2(–2.5) mm, rectangular; lower petal (18–)20–21(–23) mm × (8–) 9–11 mm, shaped as the lower case letters “b” and “d”. Anthers 5.5–7 mm long. Ovary 5–6 mm long, curved downwards, grooved, glabrous. Fruit 18–24 mm × 5–6 mm, irregularly fusiform, grooved, glabrous, with 3–10 seeds. Seeds 2–3 mm × (1.0–) 1.5–2 mm, roundish-ovate, with trichomes, sticky when fresh ( Fig. 3 ).

Habitat: —Lower rainforest belt, growing on granitic rocks along a small stream in dense lowland rainforest, 489 m ( Fig. 4 ). On Mt. Marojejy this vegetation type is found below 800 m ( Humbert 1955).

Distribution: — Madagascar, Marojejy National Park, small stream near Cascade d´Humbert ( Fig. 5), only known from the type collection.

Phenology: —Collected in flower at the type locality in October. In cultivation at the Botanical Gardens of the University of Bonn, flowers have been noted almost every month.

Etymology: —From the Greek γαλαξίας (galaxias = the milky one), referring to the “milky look” of the yellowish white, semi-transparent flowers.

Conservation status: —With only a single collecting site, it is not possible to calculate an Extent of Occurrence (EOO). The area of occupancy (AOO) covers 9 km 2 and falls within the limits for the Critically Endangered status under sub-criterion B2 of the IUCN (2001). The species is currently only known from the type locality which is within a well-managed protected area (Marojejy National Park) and is considered as safe. However, despite its restricted range, no immediate threats to the species are expected and there is no evidence for a continuing decline. Hence, I. galactica does not qualify for any threatened category, and is assessed as Least Concern (LC).

Notes: —This new species of Impatiens is a member of section Trimorphopetulum , which is characterized by the lack of spurs in the flowers and extrafloral nectaries on the petioles ( Fischer & Rahelivololona 2007a). It is probably closely related to the morphologically similar, but larger species, I. messmerae ( Fischer & Rahelivololona 2007a: 296) . The latter is also known from a similar habitat, a small stream on Mt. Marojejy but at higher elevation (750 m). However, I. galactica differs from I. messmerae in being a smaller plant (up to 35 cm vs. up to 60 cm high), being entirely glabrous and lacking small white scales (vs. whitish scales present on stems and leaves). The lateral sepals in the new species are lanceolate with obtuse apex (vs. linear-filiform with acuminate apex), the lower sepal is ovate with a pronounced abruptly tapering short apex and a 2 mm wide orange line with slight ornamentation on midrib (vs. lanceolate and gradually tapering into an acuminate apex and completely lacking any colour and ornamentation), the dorsal petal with dilated triangle placed slightly below middle towards base (vs. placed above middle towards apex in I. messmerae ), and the lateral united petals shaped as the lower case letters “b” or “d”, which are very narrow in the upper part with upper petal narrow and bearing a very short tip (vs. upper petal much larger in comparison to lower petal, rectangular, obtuse, up to half the size of lower petal).

In cultivation we noted that I. galactica produces nectar mainly in the late afternoon and evening along the orange-yellow, shiny line on the lower sepal. Furthermore, the flowers exude a pleasant, fruity-sour scent that gets stronger during the late afternoon and evening. This, in combination with the flower colour, suggests pollination by nocturnal insects.

Figures

FIGURE 1. Impatiens galactica.A, B, habit; C, flower in abaxial view; D, flower in adaxial view; E, lower sepal; F, lateral sepal; G, dorsal petal; H, lateral united petals.All drawn from the type by E. Fischer.

FIGURE 2. Impatiens galactica. A, habit; B, habit with inflorescence; C & D, flower. Photographs: S. Abrahamczyk (A), cultivated in Botanical Gardens University of Bonn; E. Fischer (B–D), Marojejy National Park, Madagascar. Scale bar = 2 cm (A & B), 5 mm (C & D).

FIGURE 3. SEM micrograph of a seed of Impatiens galactica (A); note the flattened trichomes under a film of mucilage (B). Micrograph: H.-J. Ensikat.

FIGURE 4. Habitat of Impatiens galactica, Marojejy National Park, Madagascar, Cascade Humbert. Photograph: E. Fischer.