Isolona Engl.

Couvreur, Thomas L. P., Gereau, Roy E., Wieringa, Jan J. & Richardson, James E., 2006, Description of four new species of Monodora and Isolona (Annonaceae) from Tanzania and an overview of Tanzanian Annonaceae diversity, Adansonia (3) 28 (2), pp. 243-266 : 253

Genus Isolona Engl.

ISOLONA IN EAST AFRICA

Isolona comprises 21 species occurring from Sierra Leone to northern Angola, and from Kenya to northern Mozambique. Five species are endemic to the eastern and northern coast of Madagascar. In East Africa, Verdcourt (1971) recognized three species, plus one unidentified specimen: Schlieben 1539 referred to as Isolona sp. A . He indicated that it could be a glabrous variant of Isolona heinsenii Engl. & Diels. Based on more collections by Polhill and Lovett, Verdcourt (1986) identified the specimens as Isolona hexaloba , a very polymorphic West African species ( Le Thomas 1969). Verdcourt specified however that fruiting material must be found in order to confirm its status. More collections have been made since, with fruiting material and photographs now available. On the basis of floral morphology, fruits, tectum structure, and ecology, we are now able to describe these collections as a new species. However, Schlieben 1539 from the Mahenge Mountains is excluded from it and identified as a glabrous variant of I. heinsenii as speculated by Verdcourt (1971), a species already known from that area.

Isolona species are always confined to humid regions across Africa and Madagascar, and are mainly present in the moist montane forests of Tanzania.

KEY TO THE EAST AFRICAN SPECIES OF ISOLONA

1. Flowers growing on c. 2 m long shoots running from base of trunk; fruits conical and warty, to 6 cm long .................................................................................... I. cauliflora

— Flowers on branches and axillary ................................................................................ 2

2. Leaves narrowly elliptic; densely red-tomentose .......................................... I. congolana

— Leaves elliptic to ovate; glabrous or pubescent ............................................................ 3

3. Sepals lanceolate, 5-6 mm long; corolla lobes recurved over receptacle; fruits fusiform, clearly 6-ribbed in fresh material ................................................................. I. heinsenii

— Sepals triangular, 2-3 mm long; corolla lobes spreading horizontally; fruits irregularly elliptic, with caudate apex ................................................................................ I. linearis