A new disjunct species of Eriolaena (Malvaceae, Dombeyoideae) from Continental Africa

Abstract Eriolaenarulkensii Dorr, sp. nov. is described and illustrated. This attractive shrub is endemic to coastal Mozambique. The new species has apically winged seeds, which place it in a group of Malvaceae (Dombeyoideae) that is found in Asia and Madagascar and which had not previously been found in continental Africa.


Introduction
When A.J.H. (Ton) Rulkens encountered a yellow-flowered shrub on the shore of Pemba Bay (Baia de Pemba) near the city of Pemba in north-eastern Mozambique, he could not identify it and sent photographs to John E. Burrows (BRNH) who also was unsure as to its identity. Burrows, in turn, shared photographs of the plant with several botanists including I. Darbyshire (K) who identified it as a species of Dombeyoideae (Malvaceae). Darbyshire noted that it did not match either Dombeya Cav. or Melhania Forssk., the two genera of Dombeyoideae known from the area (Wild and Gonçalves 1979;Cheek and Dorr 2007), and he observed that it closely resembled Helmiopsis H. Perrier, a genus of Dombeyoideae endemic to Madagascar. The lack of scales on the unidentified plant, however, led Darbyshire (personal communication) to doubt whether or not it belonged in that genus. Independently, photographs were sent to one of us (LJD) with a simple request for confirmation that the species belonged in the "Sterculiaceae" (i.e. Malvaceae sensu lato). An initial scepticism about this placement very quickly gave way to the realization that the photographs depicted a species that belonged to a genus of Malvaceae (Dombeyoideae) that had not yet been reported from continental Africa. More specifically, the new species appeared to belong to one of two endemic Malagasy genera, either Helmiopsis or Helmiopsiella Arènes.

Eriolaena rulkensii
Etymology. Named for A.J.H. (Ton) Rulkens, an agronomist who works for OX-FAM Belgium to strengthen small-scale farmer organizations in Cabo Delgado province, Mozambique. Rulkens is also a keen amateur botanist and photographer who has made many interesting plant discoveries in Mozambique, especially amongst representatives of the succulent flora (McCoy et al. 2014(McCoy et al. , 2017McCoy and Baptista 2016).
Distribution and ecology. Endemic to northern Mozambique where it is known from several localities on the eastern and southern shore of Pemba Bay (Baia de Pemba) near the city of Pemba where it occurs on heavy clay over coral-rag in coastal scrub at the upper margin of mangrove communities (Burrows et al. 2018); ca. 10 m alt. According to Rulkens (personal communication), Ernst Schmidt observed the shrub between Macomia and the coast in 2009 but later discovered the plant had been cut down. Rulkens also observed additional locations with many plants about 10 km from Pemba in small patches of coastal forest on fossil coral substrate.
Threats. Eriolaena rulkensii is exploited for firewood (fide Rulkens 1, in sched.) and, on a different scale, it is threatened because the coastal forests and woodlands of northeast Mozambique are subject to increased development following the instability resulting from the independence and civil wars (Timberlake et al. 2011). Eriolaena rulkensii is only one of many new species discoveries and new records from the Cabo Delgado area of Mozambique, others of which are enumerated by Timberlake et al. (2011).

Discussion
Within the Dombeyoideae, Barnett (1988b) recognized morphological and anatomical similarities that united the Asian Eriolaena and Malagasy Helmiopsis and Helmiopsiella as a group. All three genera have woody and ovoid-or obovoid-conical capsules as well as seeds with apical wings. Skema (2012) subsequently published molecular data that support the distinctive nature of this "winged-seed clade" and demonstrated that the clade was early diverging from Dombeya sensu stricto. Eriolaena rulkensii represents the first species of this "winged-seed clade" to be found in continental Africa.
Eriolaena rulkensii is not the only example of an Asian/Malagasy species that also occurs in Mozambique but is otherwise absent from continental Africa.