Crotalaria trifoliolata Baker f.

Friis, I. & Weber, O. 2014. Crotalaria trifoliolata (Leguminosae: Papilionoideae), a previously incompletely known Ethiopian endemic rediscovered after 120 years. Kew Bulletin 69: 9536. DOI https://doi.org/10.1007/s12225-014-9536-7

Type

Type: Ethiopia, ‘Somali-Land, Walenso,’ 26 Oct. 1894 [see discussion of ‘The correct position of the type locality’ above], Donaldson Smith 213 (holotype BM! (BM000843508)).

Morphology General Habit

Shrubby plant with single or several ± 0.8 m high stems from a semi-woody base, most branched in the upper part

Morphology General Bark

Bark on old stems grey, smooth, on young stems covered by a thick grey to ferrugineous tomentum

Morphology Leaves

Leaves laxly clustered towards the upper part of stems, not long persistent on older parts, often ascending at first, later spreading; internodes ± 1 cm long

Morphology Leaves Stipules

Stipules narrowly triangular to linear-caudate, 4 – 6 × 0.8 – 1 mm, tomentose

Morphology Leaves Leaf lamina

Lamina trifoliolate

Morphology Leaves Petiole

Petioles 2.5 – 4 cm long, with indumentum as on the young stems

Morphology Leaves Leaflets

Leaflets mostly obovate, sometimes elliptic, 2.5 – 5.5 × 2.0 – 3.0 cm, length 1.4 – 1.7 × width; apex rounded or emarginate, sometimes with the midvein ending in a small apical mucro; margin entire; base cuneate; lateral veins 14 – 16, mostly opposite in basal part of the leaflet, becoming alternate in the upper part and forming a lax reticulation near the margin; adaxial side densely and finely pilose with appressed or slightly spreading fine white hairs, margin with longer and more robust white hairs, which are also present on the venation of the abaxial side, shorter and finer half-appressed white hairs between the veins

Morphology Reproductive morphology Inflorescences

Inflorescences terminal or leaf-opposed, on peduncles 2 – 4 cm long, with indumentum as on the stems

Morphology Reproductive morphology Flowers

Flowers in a raceme with (10 –) 15 – 30 (– 35) flowers, which are densely packed at first (and persistently so at the tip of the inflorescence), becoming laxer during anthesis, with bracts and pedicels 1 – 1.5 cm apart

Morphology Reproductive morphology Inflorescences Bracts

Bracteoles appressed to the calyx, often fallen or difficult to see because of the dense ferrugineous tomentum of the calyx, oblong or obovate to narrowly obovate, 1.5 – 2.5 × ± 1 – 1.5 mm, with dense ferrugineous tomentum Bracts linear-caudate, 4 – 6 × 0.8 – 1 mm, finely tomentose on the abaxial side, glabrescent on the adaxial side

Morphology Reproductive morphology Flowers Calyx

Calyx broadly campanulate, 3 – 4 × 4 – 5 mm excluding calyx lobes, densely ferrugineouslytomentose outside, completely glabrous inside; calyx lobes subequal, narrowly triangular, 3.5 – 6 × 1.5 – 2 mm

Morphology Reproductive morphology Flowers Corolla

Wings 8 – 9 × ± 3 mm, slightly longer than the keel, of the same colours as the standard Standard broadly elliptic, 8 – 9 × 6 – 7 mm, glabrous outside, yellow, claw 1 – 2 mm long, slightly darker orange-yellow or tinged purplish-brown Keel abruptly rounded a little below the middle, the beak projecting and only slightly incurved at the tip, 8 – 9 mm long from insertion to the round of the up-bent tip, which is 8 – 9 mm long, glabrous except for a line of white hairs along the edge of the proximal half, colour variable from pale yellow to yellow with a purplish-brown; generally the colour of the keel is paler than the standard and wings Corolla pale to dark yellow or yellow-orange; in Friis et al-15074 with the basal parts of the standard, wings and keel sometimes tinged dark orange to brownish-purple, in Donaldson Smith 213 these parts of the flowers are sometimes tinged brighter purplish

Morphology Reproductive morphology Flowers Androecium Staminodes

Staminal tube 7 – 8 mm long

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary 6 – 9 mm long, densely white tomentose; style ± 8 mm long, bent downwards at the insertion on the ovary, curving upwards in the lower ⅓, straight in the apical ⅔, glabrous except for a line of white hairs along the upper side in the apical ⅓

Morphology Reproductive morphology Flowers Gynoecium Stigma

Stigma capitate, ± 0.3 mm in diam- Legume on 1 – 2 mm long stipe, slightly curved cylindrical with rounded ends or slightly narrowing towards the base, 28 – 31 mm long, ± 8 mm in diam., with white to ferrugineous indumentum; densely packed with tomentum of long white hairs inside, nearly filling the space between the (10 –) 12 – 15 seeds and presumably retaining them in the pod when this opens instantaneously along both sutures

Morphology Reproductive morphology Seeds

Seeds triangular cordiform, ± 1.6 × 1.2 × 0.5 mm; surface smooth or with very faint parallel or slightly irregularly placed lines, dark brown

Figures

Figs 3 & 4.

Distribution

Ethiopia, Oromia Regional State, in the BA floristic region of the Flora of Ethiopia (Hedberg & Edwards 1989). So far documented only from mountains near Sheik Hussein.

Ecology

According to our field observations Crotalaria trifoliolata seems to be restricted to edges and glades of dry Juniperus forest on limestone at altitudes above ± 1600 m a.s.l. Thulin (1989: 204), assuming that the collecting locality of the holotype was between Ginir and Sof Omar, indicated the habitat as probably dry bushland at ± 1400 m a.s.l. According to information from the type and our observations the species occurs at (?1650 –) 1850 – 2000 m a.s.l. at the edge of and in glades in dry Juniperusprocera forest growing in thin soil over limestone (Table 1; Figs 1, 2). Friis (1992) and Friis et al. (2010) argue that this type of Juniperusprocera-Olea europaea subsp. cuspidata forest on the eastern escarpment of the Ethiopian highlands and in the mountain chain in northern Somalia represents a floristically distinct vegetation type. Friis et al. (2010) called this vegetation ‘Transition between Afromontane vegetation and Acacia-Commiphora bushland on the eastern escarpment (DAF/TR),’ and determined its altitudinal range from 1500 to 2400 m and its annual rainfall range between 400 and 700 mm. Apart from JuniperusproceraEndl. and Olea europaea L. subsp. cuspidata (G. Don) Cif. in the canopy, it is characterised by Barbeya oleoides Schweinf., Cussonia holstii Engl., Tinnea somalensis Chiov. and a range of other endemic or near-endemic species in the understorey (Lovett & Friis1996).

Conservation

Crotalaria trifoliolata is listed as Endangered (EN) in Walter & Gillett (1998), based on information by Edwards & Asfaw (1992) and Thulin (1983, 1989). Vivero et al. (2005) do not mention C. trifoliolata, nor is it included in the Internet-based IUCN Red List of Threatened Species (IUCN 2013). According to our observations Crotalaria trifoliolata occurs locally in small populations at the forest edge and in open glades in Juniperus forest, where we observed it for a maximum of ± 4 km along the road. These localities are all inside the Kubayo National Forest Priority Area, of which only ± 6% is undisturbed or slightly disturbed, the rest is heavily disturbed forest, forest converted to plantations and land converted to other uses (Kidane Mengistu 2003). We observed settlements and plantations of coffee, qat and oranges inside the area of the forest priority area. A piped water supply from the mountains and the construction of the new road to Sheik Hussein will undoubtedly increase the human pressure on the Kubayo National Forest Priority Area. The fact that C. trifoliolata sometimes survives along roadsides (Fig. 2) will probably not protect it from that pressure. Using our field data and the MaxEnt model prediction (which adds the isolated mountains with limestone within the red square in Map 2 to the area), we estimate the Extent of Occurrence to be less than 1500 km2. The Area of Occupancy based on the auto-value of 6 km cell-width is 164 km2, or 32 km2 using the cell size recommended by IUCN. The area-calculations were carried out using the Geo-Cat tool (Bachman et al. 2011), using the distributional data in Table 1. The modelled distribution is fragmented and we assume from our field observations that the sub-populations are limited in size. The habitat in general is degraded or partly destroyed from road building, cattle grazing and growing pressure from settlements. Based on this we evaluate the species as Endangered (EN), meeting IUCN criterion B1ab(iii) and B2ab(iii) (IUCN 2012).

Phenology

Flowering time: Oct. to Dec., possibly longer. Fruiting time: Dec., possibly longer.

Note

Our additional information, however, does have relevance for the position of Crotalaria trifoliolata within the subsection. In the key of Polhill (1982: 159), C. trifoliolata keys out in the second lead of couplet 23: ‘Legumes glabrous inside …’ Due to our observation of mature pods, C. trifoliolata must instead key out in the first lead of couplet 23: ‘Legumes (and ovary) packed inside with long hairs …’ and the words ‘stipules absent’ in that couplet must be deleted. C. trifoliolata will then fall in a group of species with long hairs inside the pod (C. leucoclada Baker, C. rhynchocarpa Polhill, C. saltiana Andrews and C. thomasii Harms). This group of species, now also including C. trifoliolata, all occur in or adjacent to the Somalia-Masai regional centre of endemism (White 1983), which extends from Ethiopia and Somalia through Kenya to northern Tanzania. In the protologue (Baker 1896: 53) and in a subsequent taxonomic revision of the genus Crotalaria Baker (1914: 362) compared his new species with the widespread C. incana L. and C. deflersiiSchweinf. C. trifoliolata was accepted and given full treatment in the monograph of the genus in Africa and Madagascar by Polhill (1982: 170), also providing a new description of the holotype. Polhill placed the species in sect. Hedriocarpae Wight & Arn. subsect. Hedriocarpae, next to C. deflersii and C. comanestianaVolkens & Schweinf. The new information does not change the general classification proposed by Polhill (1982: 15). According to our observations C. trifoliolata again keys out as belonging to sect. Hedriocarpae subsect. Hedriocarpae due to the short receptacle, the beak of the keel not being twisted, the simple, curved style and the rather uniformly yellow petals. Given the presence of stipules in Crotalaria trifoliolata, it can be keyed out as the first species after the first lead of couplet 23. C. trifoliolata is somewhat similar to C. leucoclada in habit and stem-indumentum, but differs in the presence of stipules, in having more pilose and larger leaflets (2.5 – 5.5 × 2.0 – 3.0 cm versus 1.5 – 3.5 × 0.6 – 1.8 cm) and in the pods being 28 – 31 mm long, rather than ± 16 mm long. Apart from the presence of stipules, C. trifoliolata differs from the other species in the group with hairs inside the pod in being an erect subshrub with persistent bracts and bracteoles, rather than a spreading bushy plant (C. saltiana) or a plant with long procumbent branches (C. thomasii), or having early caducous bracts and bracteoles (C. rhyncocarpa). Crotalaria leucoclada, the species which morphologically is most similar to C. trifoliolata, has been known only from a few collections made by the end of the 19th century in the mountains of northern Somalia (Polhill 1982: 172; Thulin 1993: 450), but an additional specimen was collected in 1983 from the western escarpment of the AsirMts in Saudi Arabia by Iris Sheila Collenette and annotated by R. M. Polhill as C. leucoclada in 1983 (Collenette 4600; http://elmer.rbge.org.uk/bgbase/vherb/bgbasevherb.php?cfg=bgbase/vherb/zoom.cfg&filename=E00277122.zip&queryRow=1). Comparison of Collenette 4600 and Friis et al. 15074 clearly confirms the distinction between C. trifoliolata and C. leucoclada.

International Legume Database and Information Service

Conservation

Insufficiently known

Morphology General Habit

Not climbing, Herb