Otholobium is a genus of flowering plants in the pea family with over 50 named species, but several also remain undescribed so far.[1] Species may be herbaceous perennials, subshrubs, shrubs or small trees. The alternately set leaves are accompanied by stipules and mostly consist of three leaflets, sometimes just one. The inflorescences are on short or long stalks in the axils of the leaves. Within the inflorescences, the pea-like flowers occur in groups of three, rarely of two, subtended by a bract, and each individual flower also is subtended by a narrow bract. The petals may be white, pink, purple or blue, often with a differently colored nectar guide, that may sometimes even be yellow. The seedpods contain just one, black, dark or light brown seed. Most species are restricted to the Cape provinces of South Africa, but some occur at higher elevations in eastern Africa. Charles Stirton erected the genus in 1981.[2] The species in South America will probably be segregated, because these are not sufficiently related to the African species.[3]
Description
leaf with stipules and 3 entire leaflets in O. obliquum
As far as known, the species currently assigned to the genus Otholobium are diploids with 20 chromosomes (2n=20). They are shrubs, subshrubs or sometimes spreading herbs with alternately set leaves, each consisting of one or three entire leaflets carrying black or transparent glands, which have a wedge-shaped base and a pointed or blunt tip that is often hooked, with the main vein extended beyond the tip. Left and right of the base of the leafstalk, are two softly hairy stipules that may be partly merged with the stalk or entirely free, and are oval with a pointy tip or awl-shaped, while several veins create a striped appearance.[2]
Flowers in a cluster of 3 in O. obliquum
The flowers are seated or on a very short stalk, growing in inflorescences consisting of 1 or 5-18 groups of 3 or rarely 2, set in the leaf axils or at the tip of the stems. Every individual flower is subtended by a bract and every triplet is subtended by an oval bract. The 5 sepals are merged at the base to form a bell-shaped calyx and 5 unequal lobes at the top. The lowest lobe may or may not be much longer or broader than the rest, while the upper 2 or 4 lobes may be merged further toward the tip. The inside of the calyx is sometimes covered in black, stubby hairs.[2]
As in most Faboideae, the corolla is zygomorph, forms a specialized structure and consists of 5 free petals. These may be white, yellow or pale blue in color. The upper petal, called the banner or standard, is large and envelops the other petals in the bud. It is oblong or oval in shape, with weakly developed claw and auricles and no appendages. The 2 adjacent petals called wings have long claws, are tinged purple at the blunt tip, are adorned by ridges, and enclose the 2 bottom petals. The two bottom petals have long claws and are tinged purple at the blunt tip, are free at the base but fused together at their tip and they form a boat-like structure called the keel. In Otholobium, the keel is much shorter than the wings. The keel contains 10 identically shaped filaments, 9 are fused while 1 is partially free. The anthers are alternately fixed to their filament at the base and at midlength. The seated ovary is either covered in hairs or in glands and contains 1 ovule. It carries the swollen style that is topped by a pin-shaped stigma, without or with a brush of hairs. From it develops a swollen, softly hairy fruit that ends in a slight beak and protrudes from the calyx when ripe. The fruit does not open. The seeds are light brown to black in colour and longer than wide.[2]
Differences with related genera
Otholobium differs from Psoralea and Hallio by the lack of a cupulum, a small, 2- or 3-lobed bract that encircles the peduncle between its base and the calyx. It differs from Cullen, which has a black glandular-warty fruit.[4]
Carl Linnaeus was the first to describe a species now assigned to this genus, and he called it Trifolium fruticans. It is now known as Otholobium fruticans. This name was published in the Species Plantarum in 1753, the first work to consistently apply binomial names. Two further species were described by Carl Linnaeus the Younger in 1781. He named them Psoralea rotundifolia and P. stachydis, and these species are now known as Otholobium rotundifolium and O. hirtum. This was followed in 1794 by Jean Louis Marie Poiret who added P. acuminata, P. ononoides and P. sericea, which are currently named O. acuminatum, O. virgatum and O. sericeum respectively. When Carl Thunberg, who visited the Cape from 1772 till 1775, revisedPsoralea in 1823, and therein added P. tomentosa, P. racemosa, P. argentea and P. striata (now O. sericeum, O. racemosum, O. argenteum and O. striatum). Ernst Heinrich Friedrich Meyer described in 1832 Psoralea obliqua (now Otholobium obliquum), P. bracteata var. bracteata (now O. fruticans) and P. bracteata var. brevibracteata (the current O. bracteolatum). In 1836, Psoralea was reviewed by Christian Friedrich Ecklon and Karl Ludwig Philipp Zeyher, who distinguished P. albicans (= O. argenteum), P. algoensis and P. bracteolata (which are considered to be conspecific and are known today as O. bracteolatum), P. candicans (now O. candicans), P. cephalotes and P. stachyerum (both now included in O. stachyerum), P. hilaris (currently O. racemosum), P. polyphylla (now O. polyphyllum), P. rupicola (now included in O. striatum), P. uncinata (now O. uncinatum) and P. venusta (now O. venustum). In the same year Meyer published a revision in which he distinguished P. carnea, P. obliqua, P. parviflora, P. triantha (now known as O. carneum, O. obliquum, O. parviflorum and O. trianthum respectively), P. cephalotes (= O. stachyerum), P. densa (= O. acuminatum), and P. spathulata (= O. mundianum). In Volume II of the Flora Capensis, published in 1862, William Henry Harvey newly described P. bowieana, P. hamata, P. macradenia, P. polysticta and P. thomii (now O. bowieanum, O. hamatum, O. macradenium, O. polysticum, O. thomii). Daniel Oliver described Psoralea foliosa (= O. foliosum) in 1885, while Edmund Gilbert Baker distinguished P. foliosa var. gazense (= O. subsp. gazense) in 1911. Helena Forbes added in 1930 P. bolusii (= Otholobium bolusii) and P. royffei (included in O. caffrum). Henry Georges Fourcade described P. heterosepalum (= O. heterosepalum) in 1932.
The genus Otholobium was erected in 1981 by the British/South African botanist Charles Stirton. He chose Psoralea caffra as type species. He reassigned many species previously included in Psoralea to his new genus and described many new species since then: Otholobium pungens in 1981, O. rubicundum and O. pictum in 1982,[2]O. swartbergense in 1986,[5]O. accrescens, O. arborescens, O. dreweae, O. flexuosum, O. fumeum, O. incanum, O. lanceolatum, O. lucens, O. nigricans, O. nitens, O. prodiens, O. pustulatum, O. sabulosum, O. saxosum and O. spissum in 1989.[2][3][6] He described O. fumeum and O. nigricans from Natal and Transvaal in 1990.[7]
O. curtisiae was described in 2013 by Stirton together with A. Muthama Muasya.[9] These two authors further described O. accrescens, O. dreweae, O. lanceolatum, O. lucens, O. nitens, O. piliferum, O. prodiens, O. sabulosum, and O. saxosum in 2017.[10]
The name of the genus Otholobium is a combination of the Greek words ὠθέω (ōthéō) meaning to push and λοβός (lobos) meaning pod, which Stirton selected because its fruit seems to be pushed out of the calyx.[11]
Phylogeny
Comparison of homologous DNA has increased the insight in the phylogenetic relationships. The following tree represents current insight in the relationship within the Psoraleeae.[3]
Almost all species assigned to the genus Otholobium are limited to the Cape provinces of South Africa, but a few can be found outside South Africa along the continent’s east coast to Kenya. O. foliosum subsp. gazense occurs in the Chimanimani Mountains along the Zimbabwe-Mozambique border, and O. foliosum subsp. foliosum in the mountains of Malawi, Tanzania and Kenya. The genus is absent from Ethiopia and Madagascar. Like in many other plant genera, species density dramatically decreases to the east and north of the West Cape province.[2] The species assigned to the genus by Grimes occur in the Andes from Chile in the south to Colombia and Venezuela in the north.[8]
Finally, three taxa have not been evaluated, O. argenteum because not enough information was available to determine its conservation status, O. prodiens because there is doubt about its status as a species and O. foliosum subsp. foliosum because it does not occur in South Africa.[12]
Related Research Articles
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The tribe Psoraleeae is one of the subdivisions of the plant family Fabaceae. Recent phylogenetics has this tribe nested within tribe Phaseoleae.
Vexatorella is a genus containing four species of flowering plant, commonly known as vexators, in the family Proteaceae. The genus is endemic to the Cape Floristic Region of South Africa. The name means “little trouble-maker”, given with reference to the initial difficulties of placing V. latebrosa within the family. All species are shrubs which occur in dry fynbos habitats on the fringes of the Succulent Karoo ecoregion. The inflorescences are similar to those of the related leucospermums but also share features of the leucadendrons, with the floral bracts becoming woody and enlarged following pollination. The flowers are insect-pollinated, with the seeds dispersed by ants (myrmecochory).
Petalidium, commonly known as petal-bushes, is a genus of perennial shrubs in the acanthus family. They are native to sandy flats or stony slopes in the drier bush regions of Africa, India and the Mascarene Islands. The majority of species occur in frost-free, summer rainfall regions of southern Africa, and may be found from low to medium altitudes.
Schoenus bolusii is a species of sedge endemic to the mountains of the Western Cape Province of South Africa. However, S. bolusii is not found on the Cape Peninsula.
Otholobium swartbergense is a small spreading shrub assigned to the Pea family. All green parts are covered in hairs. It has many slender stems that are woody at their base, alternately set clover-like leaves and heads consisting of 6-15 mauve to purple, pea-like flowers on long peduncles in the axils of the leaves. This species is an endemic of the Swartberg mountains in the Western Cape province of South Africa. It mostly flowers in November and December.
Otholobium curtisiae is a small spreading shrub assigned to the Pea family. All green parts are covered in hairs and urn-like glands. It has many woody stems, small and somewhat succulent, dark green alternately set clover-like leaves and heads consisting of 3-9 white, pea-like flowers on very short peduncles in the axils of the leaves. This species is an endemic of the Overberg area in the Western Cape province of South Africa. It mostly flowers in August and September.
Otholobium dreweae is an upright shrublet assigned to the Pea family of about 15 cm (5.9 in) high, that appears after the vegetation burned down from the underground rootstock and forms mat-like clumps of hardly branching, leafy stems. The stems are set with stiff, entire, alternate leaves with a single leaflet and heads consisting of 12-18 initially dark pink, later white, pea-like flowers with a white nectar guide on a peduncle as long as the leaves at the end of the stem. This species is an endemic of the Kleinrivier Mountains in the Western Cape province of South Africa. It mostly flowers in November.
Otholobium accrescens is an upright, largely herbaceous subshrub assigned to the Pea family. It has up to three stems that carry upright branches in leaf axils near the ground, and have alternately set inverted egg-shaped leaves and lax heads consisting of 12-21 pea-like flowers on long peduncles in the axils of the lower leaves. It differs from most other Otholobium species by the calyx that continues to grow after flowering and the leaf that consists of just one leaflet. It is an endemic of the Eastern Cape province of South Africa near Loerie. It probably flowers August to January.
Otholobium nitens is an upright, densely branched shrub of up to 1.5 m high that is assigned to the Pea family. It has one to many initially softly hairy stems, alternately set, clover-like, upright leaves crowding the new shoots, and heads consisting of 3 pea-like, dark purple to mauve flowers on short peduncles in the axils of the leaves on short side-shoots. This species is an endemic of the mountains between Ceres and Hottentots Holland in the Western Cape province of South Africa. It mostly flowers between October and late December.
Otholobium saxosum is a small shrublet of up to 20 cm (7.9 in) high that has been assigned to the Pea family, with branches upright or horizontal at the base with rising tips. It has sessile, clover-like leaves and white, pea-like flowers that grow in triplets in the axils of the upper leaves of new, short side shoots. The species is only known from Garcia's Pass in Western Cape province of South Africa. Flowering occurs in October and November.
Otholobium spissum is a dense, tangled, much branched shrub of up to 185 cm (73 in) high that is assigned to the Pea family. It has dull green, clover-like leaves and white, pea-like flowers with a streaky, triangular, purple nectar guide. The species grows in renosterveld in the central mountains of the Western Cape province of South Africa. This species flowers in July and August.
Otholobium lanceolatum is a small subshrub of up to 20 cm (7.9 in) high, that is assigned to the Pea family. It has up to 7 horizontal stems with raised tips, few hairless, alternately set leaves with only one leaflet and clusters of 15-27 white, pea-like flowers with a purple tip near the top of the short, seasonal shoots. It is endemic to one site near Caledon, South Africa. Flowers only appear in November and December within one year after a fire destroyed the vegetation.
Otholobium lucens is a shrub of up to 60 cm (24 in) high that is assigned to the pea family. It has alternately set clover-like leaves crowding on the new growth, while older parts have lost their leaves. The white, pea-like flowers occur with 3 or 6 together in the leaf axils. This rare species is an endemic of the Swartberg mountains in the Western Cape province of South Africa. It flowers between July and February.
Otholobium piliferum is a small, softly hairy shrublet of up to 30 cm (12 in) high that has been assigned to the Pea family, with branches horizontal at the base with rising tips. It regrows from the underground rootstock after fire destroys the vegetation. It has clover-like leaves on short stalks and white, pea-like flowers flushed with mauve that grow in triplets in the axils of the upper leaves of the new shoots. The species is only known from near Makhanda, Eastern Cape province of South Africa. Flowers have been seen in September and January. This is a very rare species about which little is known and which is likely threatened with extinction.
Psoralea fascicularis, the large-stipule fountainbush, is a species in the pea or Fabaceae family. It is endemic to the Western Cape province of South Africa where it has been red listed as endangered (EN) by the International Union for Conservation of Nature (IUCN) Red List of Threatened Species due to its declining population.
Dianthus albens is a species of flowering plant in the family Caryophyllaceae.
Dianthus thunbergii is a species of flowering plant in the family Caryophyllaceae.
Selago thomii is a species of plant in the family Scrophulariaceae. It is endemic to the Western Cape, South Africa.
References
↑ C.H. Stirton; A.L. Schutte (2012). "Psoralea". In J. Manning; P. Goldblatt P. (eds.). Plants of the Greater Cape Floristic Region 1: the Core Cape Flora. Strelitzia. South African National Biodiversity Institute. pp.571−575.
↑ Manning, John; Goldblatt, Peter (2012). Plants of the Greater Cape Floristic Region 1: the Core Cape flora. Strelitzia. Vol.29. Pretoria: South African National Biodiversity Institute. p.519.
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