Hibiscus hareyae L.A.J.Thomson & Cheek, 2020

Thomson, Lex A. J. & Cheek, Martin, 2020, Discovered online: Hibiscus hareyae sp. nov. of sect. Lilibiscus (Malvaceae), threatened in coastal thicket at Lindi, Tanzania, Kew Bulletin 75 (4), pp. 3250-3252 : 3-8

Hibiscus hareyae L.A.J.Thomson & Cheek sp. nov.

Type : Tanzania, Lindi Province, “Collected July 1877. Lindi, E. Africa, Lat. 9 40’ South this extends its habitats a little further South than before”, Kirk s.n. (holotype K00240493 !) ( Fig. 1 ) .

http://www.ipni.org/urn:lsid:ipni.org:names:77213108-1

Syn. Hibiscus schizopetalus auct., non (Dyer) Hook.f. sensu Mwachala (2009: 60) pro parte

Deciduous erect, sprawling, to scandent shrub, 2 – 4 m tall, to 6 m wide, often leafless or near-leafless at onset of flowering. Branches slender, pendulous arching to the ground; bark grey with white blotches. Branchlets light grey-green, becoming waxy-white, smooth or finely ridged, 2 – 3 mm diam., internodes 1.2 – 1.8 (– 4.5) cm long, glabrous. Leaves deciduous during the dry season; light green above, ovate, oblong or elliptic, 1.8 – 3.0 (– 4.7) × 0.9 – 1.5 – 1.8 (– 3.5) cm, apex obtuse-rounded, base obtuse, finally abruptly rounded, nerves palmate at base, midrib with 2 – 3 secondary nerves on each side of the midrib, nerves prominent below; teeth (1 –) 3 – 5 (– 10) per side, large rounded-crenate, 1 (– 2) × c. 2 – 3 (– 5) mm, margin slightly thickened, lined with appressed, simple, stout, colourless unicellular hairs c. 0.3 mm long, abaxial surface of leaf with pale golden stellate hairs thinly scattered, 0.3 (– 0.5) mm diam., arms appressed, stout. Stipules brown-purple, glossy, broadly triangular, 0.5 – 1.25 × 0.5 – 1 mm, sparsely hairy, persistent for several nodes from stem apex. Petiole 3 – 6 (– 50) mm long, slightly canaliculate, densely pubescent with long, white, sinuous simple hairs 0.3 mm long, tapering to a long acute apex. Flowers often on leafless branches, 6 – 8.5 cm wide, solitary or more typically clustered in upper leafless axils on pendant peduncle-pedicels. Pedunclepedicels stout 0.4 – 2 (– 4.5) cm long, longitudinally ridged, sparsely puberulent with a mixture of stellate and simple hairs, stellate hairs 3 – 7-armed, 1 – 2.5 mm wide, simple hairs patent, 0.5 – 1 mm long, when immature densely papillate with multicellular papillae 0.05 mm long. Epicalyx bracts 7 – 8, united at base forming a shallow cup 0.5 – 1 × 2 – 3 mm, bracts pale green, 1.5 – 4 × 1 – 1.2 mm, narrow-lanceolate, outer surface sparsely covered (c. 10% of surface) mainly in stellate hairs 3 – 4- armed, 1 – 2 mm long, simple hairs 0.5 – 1.5 mm long. Calyx pale green, slightly campanulate, tube c. 2 cm long × 4 mm wide at base to 1 cm wide at apex, 3 – 4-lobed, lobes triangular 4 – 5 mm long, outer surface sparsely covered (10 – 20% of surface) in mainly simple, patent hairs 0.5 – 1 mm long, with a few stellate hairs (as epicalyx). Petals 5, shortly clawed, claw c. 0.3 × 0.2 cm, laterally compressed, blade ovate-elliptic, c. 3 – 3.5 × 2.5 – 3 cm, pinnatifid, divided 1 = 2 – 2 = 3 to the midline, c. 8 segments each side, with the distal segments 1 – 2 mm wide and bifid or trifid, basal segment pair, oblong, 1 – 1.3 × 0.5 cm, segments slightly recurved, adaxial surface deep rose-pink or burgundy red, with an extensive (50 – 75%) white/pale pink basal zone, abaxial surface rosecrimson, also described as red (Kayombo 4590, MO) or red and yellow (Semsei S633, K). Staminal column (4 –) 5 – 6 cm long, rose pink, slender, antheriferous in terminal 25 – 30%. Stamens 100 – 110, filaments 7 – 10 mm long, pink, anthers orange, oblong 7 – 9 × 5 – 6 mm, pollen yellow or orange. Style exserted c. 1 cm beyond androecium, then dividing into 5, slender, spreading branches, c. 14 – 20 mm long, crimson. Stigma pads minute-capitate, c. 1 mm diameter, crimson. Fruit 5- valved capsule, c. 2.2 cm long × 0.8 cm wide, pale-green, valves acuminate. Seeds unknown. Figs 1 – 3 .

RECOGNITION. Within Hibiscus , H. hareyae and H. schizopetalus are the only two species with laciniate petals. Hibiscus hareyae is readily distinguished from H. schizopetalus by its much shorter and non-articulated peduncle-pedicels (0.4 – 2 cm long vs 8 – 14 cm long and articulated); longer and broader epicalyx bracts, (1.5 – 4 × 1 – 1.2 mm vs 0.6 – 1.5 × 0.1 – 0.3 (0.5) mm, the epicalyx forming a shallow cup 0.5 – 1 × 2 – 3 mm, vs bracts appearing free (for additional diagnostic characters see Table 1 ).

DISTRIBUTION. Tanzania ( Map 1 ). The species is endemic to the Kilwa and Lindi Districts (Lindi Region) of southern Tanzania. It is possible that the species might yet be found in northern Mozambique but it was not recorded as wild there by Exell (1961).

SPECIMENS EXAMINED. TANZANIA. Lindi Province: Kilwa Distr., T8 – N end of Mbarawala Plateau , 7 Nov. 2003, C. J. Kayombo 4590 ( MO 5750577 image!); Kilwa Distr., Kilwa South – pt451 , 0908S, 3920 E, fl. 25 Nov. 2003, W. R. Q. Luke & O. Kibure 9718 ( MO5792757 image!, FTG122084 image!) ( EA, K000593145 !, LMA, NHT); Kilwa Distr. , 32 km N of Lindi, Mchinga S, pt 552, fl. 20 Dec. 2003, W. R. Q. Luke & O. Kibure 10203 ( FTG122085 image!) ; Lindi Distr., c. 6.5 km N of Lindi , fl. 9 Dec. 1955, E. Milne-Redhead & P. G . Taylor 7481, 9 Dec. 1955 ( BR image!, K000593143 !, K000593144 !); Lindi, “Lat. 9 40’ South, this extends its habitats a little further South than before”, fl. July 1877, Kirk s.n. (holotype K000240943 !); Lindi, fl. Nov. 1877, Kirk s.n. ( K000593146 !); Lindi, 40 km westlich, 200 – 250 um. Mangrovenrade, fl. 26 Aug. 1934 ( Schlieben 5184 ( BM!, P06593493 image!); Lindi Region, Lindi Distr., Lindi Creek , 10 00’S, 39 44’E, fl. 15 July 1995, G. P. Clarke 89 ( K000593147 !); Lindi Distr., Lindi Township, fl. Jan. 1952, Semsei S633 ( K000593148 !); Lindi, at Mdenga, coastal hills, fl. buds, 26 Feb. 1936, Litchfield 5457 ( K000593149 !, K000593150 !); Lindi Region, Mtama Distr. , Sudi Village 10.16019E 39.96873S, fl. 12 Jan. 2020, O . Suleiman, Darbyshire & Shah, Mbailwa 5526 ( DSM, K, NHT) .

HABITAT. Hibiscus hareyae is found in coastal habitats (“in the mangrove formation” Semsei S633), in the ecotone between mangrove and thicket on coral rag (Suleiman et al. 5526) and in “coastal thicket” (Luke & Kibure 9718) or “coastal deciduous bushland” (Milne- Redhead & Taylor 7481) on the edge of seasonally-dry watercourses in thicket, and on hillsides (sea-level to 250 m alt.). There is a single record in “dry forest”. Associated species (Suleiman et al. 5526) are Fimbristylis sp.; Euphorbia tirucalli Thunb. , Dalbergia melanoxylon Guill. & Perr. , and Erythroxylum emarginatum Thonn.

Temperatures in the Lindi Region are rather constant throughout the year, with the mean daily temperature ranging from 25 – 28o C, and mean daily maximum temperature of 31 – 32o C, and mean daily minimum temperature of 20 – 24o C. The average annual rainfall is around 900 mm falling between Dec. and April, with a pronounced dry season of 6 – 7 months. Tropical cyclones, sometimes severe and reaching category 4, occur infrequently from late Dec. through to mid-April.

Hibiscus hareyae mainly occurs (Kilwa, Lindi and Kiswa areas) on coral rag, a rubble-like limestone formed by uplift of former marine coral reefs.

CONSERVATION STATUS. Hibiscus hareyae is known from 12 specimens and six threat-based locations. We calculate the area of occupancy as 40 km 2 using the 4 km 2 cells favoured by IUCN (2012). The main location is the town of Lindi, from which (or very nearby) seven collections, from at least five sites have been made. Two of these records refer to the species as occurring in mangrove where it is “very common” (Schlieben 5184 and Semsei S633). Other than these collections, there are few data on frequency, but recent research has reported it as infrequent: during the survey of thicket on coral rag resulting in collection of Suleiman 5526, H. hareyae was only seen at a single site with just 4 or 5 individuals. Although this species was targeted by the survey and other areas of coral rag were studied, no further plants were found despite it being then spectacular in flower (Darbyshire, RBG, Kew, pers. comm. to Cheek Jan. 2020). Threats from agriculture to thicket on coral rag substrate are low because coral rag is uncultivatable. However large areas within the range of the species along the coast have been converted to salt pans which appears to have destroyed habitat. Several historic sites at Lindi may have been lost due to house and road construction resulting from expansion of the town. At the site of Suleiman et al. 5526, much of the habitat had been cleared by cutting. Despite this, large areas of coral rag remain with deciduous thicket more or less intact and so H. hareyae although threatened to some degree, does not seem at present at risk of imminent extinction across its range. We advise that some of this overlooked habitat and its threatened species be protected, perhaps as part of a national Important Plant Areas programme ( Darbyshire et al. 2017). H. hareyae also ought to be conserved ex situ including through seedbanking and bringing into cultivation as an insurance policy against the species becoming extinct in the wild as is believed to be the case for other Tanzanian species such as Kihansia lovettii Cheek ( Cheek 2004) , which has never been seen since it was first collected, despite dedicated searches over several years.

PHENOLOGY. Hibiscus hareyae has been recorded as flowering from Nov. through to Feb. and July and August. Immature fruits have been observed in Nov., with the main fruiting period likely to extend from Dec. to March.

ETYMOLOGY. The specific epithet honours Dr Hareya Fassil (12 Jan. 1968 – present) in recognition of her work on conservation of plant genetic resources and the roles of traditional plant-based medicines in Africa.

VERNACULAR NAMES. Mgongonyoka (Swahili) and Kinyoka (Yau) (both Litchfield 5457); Lindi hibiscus (English).

NOTES. The holotype of Hibiscus hareyae is barcoded K000240493. It consists of two short stems both with flowers. It is mounted in the top righthand corner of a sheet at Kew with the pencilled label in the hand of Kirk, separated at the very base of the sheet, also on the right-hand side. Above this label is a separate collection, a paratype, barcoded K000593146 , of a single flower in a packet annotated in the hand of J. Hooker “ Lindi , E.Africa , Dr Kirk, Nov. 1877 ” to which the barcode K000593146 has been assigned. To the left of the label is a larger packet containing the folded manuscript note by Kirk that was published as Kirk & Oliver (1877). It is annotated in the hand of Oliver “Memorandum by Dr Kirk (18 Nov/74) to accompany specimens of Hibiscus from Mombasa” and “To be returned to Prof. Oliver” .

Below the holotype is a label in the hand of Oliver stating “Sir J. Kirk distinguishes 2 vars (letter 10 Jan. 84). 1 from Kilwa (South! Shrub erect, often leafless at flowering- unjointed in pedicel- this is the var. sent herewith. Recd. At Kew/84.”

Hibiscus hareyae is similar to H. schizopetalus , and we postulate that both species are likely ancestral within sect. Lilibiscus . It is likely that H. hareyae shares a recent common ancestor with H. schizopetalus since they are in geographic proximity, and are so morphologically similar that they have been considered to be conspecific for 150 years. We hypothesise that a single population formerly extended along the coast from Kenya to southern Tanzania, adapting to the different local environments at northern and southern extremes, becoming separated from each other due to extinction of the intervening populations. The northern evergreen plants, i.e. H. schizopetalus are confined to the shady, damp understorey of coastal semi-evergreen forest of hills, especially Kaya forests, while the southern ( H. hareyae ) is restricted to the drier habitats of deciduous coastal thickets, and appear to be more xerophilous, with smaller leaves and are at least partly and briefly themselves deciduous. Similar species-pair disjunctions between SE Kenya and S-Central Tanzania are seen in the genus Ancistrocladus ( Cheek et al. 2000) . New species to science continue to be discovered steadily in Tanzania (e.g. Cheek & Bridson 2019), including new taxa of Hibiscus e.g. H. kabuyeana Mwachala ( Mwachala 2009) and H. vitifolius subsp. lukei ( Mwachala & Cheek 2003) .

Figures

Map 1. Hibiscus hareyae. Global distribution map.

Fig. 1. Hibiscus hareyae. Image of the holotype (K00240493), Kirk s.n. Tanzania, Lindi, July 1877.

Fig. 2. Hibiscus hareyae. A habit, leafy shoot; B full-sized leaf, abaxial surface; C flowering shoot; D petal; E anther; F anther, inner face; G anther, dorsal face showing filament insertion; H pedicel, epicalyx and calyx; J pedicel detail-indumentum; K calyx margin – indumentum; L epicalyx lobe — indumentum. From Milne-Redhead & Taylor 7481. DRAWN BY ANDREW BROWN.

Fig. 3. Hibiscus hareyae. A leaves and inflorescence from above showing epicalyces; B flower from below showing white inner petal markings. From Suleiman et al. 5526 (K). PHOTOS: A IAIN DARBYSHIRE, B TORAL SHAH.