Adenium obesum is widespread and variable in its natural habitat. It occurs in a broad band across sub-Saharan Africa from Senegal to Sudan and Kenya.. It has a relatively long summer blooming period and can be kept in growth through winter in a warm and bright location. It is the most widely available species in cultivation and has been used as one of the parents in many of the hybrids. The flowers are variable in size and the plant eventually develops a very fat trunk. This extremely variable species occurs mainly north of the equator, extending southwards to Tanzania and northwards to Ethiopia, Somalia, the Arabian Peninsula and the island of Socotra. It occurs across the southern Sahara to western tropical Africa. Many of the forms included in the species have previously been described as separate species. A number of subspecies are recognized. The deciduous, succulent shrubs or small trees are 1-4 m tall. One to a few erect, smooth stems arise from a swollen base and taper towards the apex where several short, spreading to erect branches are produced. The obovate and elliptic leaves are 80-100 Í 30-35 mm, with a short petiole, and are clustered at the tips of the branches The name obesum is derived from the Latin word that means fat or fleshy, referring to the habit of the stems.
Adenium swazicum comes from Swaziland and adjacent areas in eastern South Africa and Mozambique. The flowers are uniform in color, varying from pale to deep pink to pinkish purple. Blooming is normally for a few months . The stems tend to droop, especially in plants that are too shaded. Larger plants have massive roots and thick trunks.. It is a small shrub, up to 650 mm tall, with a large, buried, succulent stem. The stem produces several greenish white or dirty-grey branches. The simple leaves are long, tapering and smooth, 40-130 Í 7-30 mm, and borne in terminal clusters. They are often folded, broader at the apex than at the base and the midrib is prominent beneath leaves .Adenium multiflorum is distinguished from A. swazicum by the upper portion on the inside of the corolla that is hairy and not smooth, by the dark border on the petals and by the flowers that usually appear before the leaves (in A. swazicum. Its range extends into highlands that have fairly cold winters; this species will tolerate a light frost with little or no damage. They also experience winter rains, so they are tolerant of being simultaneously wet and cold. White flowers are known in cultivation. Some says that wild plants may have red flowers, but they seem to be unknown in cultivation. This species is probably the second most popular in cultivation after A. obesum and a parent of many hybrids.
Adenium somalense is from Somalia south, Kenya and Tanzania. In Somalia and adjacent areas of Kenya this plant becomes a small tree, to 15 feet tall, with a massively swollen trunk. In other areas, it is more shrubby and similar to A. obesum. The flowers are a bit smaller but similar to A. obesum.).. Only A. arabicum (some populations) and socotranum have larger caudexes. The flowers are rather small especially considering the size of the plant. The most identifiable characters are the conical caudex, light-colored veins in the leaves, and nectar guides that extend onto the petal bases. This species is extremely intolerant of cold. Temperatures below 50° F (10° C) for a few weeks will usually cause the roots to Even keeping the plant dry in winter will not reliably prevent this collapse. Probably for this reason and because of its large size it is not common in cultivation.
Adenium crispum occurs in a band of sandy soil near the coast ot southern Somalia. In nature the fusiform caudex is subterranean. Most of the root system arises from near the top of this caudex. In cultivation the caudex is raised above soil level; fortunately the caudex is capable of rerooting from the bottom. The stems are thin and rarely exceed a foot tall. The small flowers are very distinctive and serve as the best identifier: most clones have quilled petals that are whitish with strong red lines extending from the throat to the margins. Some have flat petals, while some have solid red petals. This species is as sensitive to cold as A. somalense. They are also intolerant of hot, humid conditions. For these reasons it is not widely cultivated despite the beautfiul flowers and compact size.
Adenium arabicum, comes from the Arabian Peninsula, in particular from Saudi Arabia and Yemen.. One form, from Saudi Arabia, is quite tall, up to 12 feet, and somewhat similar to A. somalense. The other form is low, with somewhat reclining stems branching from a spherical basal caudex that can be as much as 3 ft. in diameter. Plants grow rapidly and develop large caudexes in only a few years.. Better clones flower sporadically throughout the year.
Adenium multiflorum is different in comparision to obesum. It has a more slender trunk than A. obesum,. It blooms for 3-4 months in winter, without leaf. The flowers are abundant and possibly the most striking of the entire group… It is found in South Africa (northern KwaZulu-Natal, eastern Mpumalanga and Limpopo), eastern Swaziland, Mozambique and Zimbabwe, extending into eastern and western tropical Africa to Malawi and Zambia. It is the most attractive species, being a deciduous thick-stemmed shrub up to 3 m tall. The leaves are, glossy green above, paler beneath, with the midrib and lateral veins distinct above, only the midrib prominent below. They are crowded at the tips of branches, are broadly oval and appear shortly after flowering.. Flowering time is May to August. The name multiflorum is derived from Latin and means many-flowered. It has the second largest leaves in the genus.. multiflorum is not widely grown. Because it grows slower than A. obesum.
Adenium boehmianum is the most western species, coming from northwestern Namibia and southern Angola. This is a slow-growing species, and must be several years old before flowering. The flowers are usually of a uniform pale. Adenium boehmianum appears to be related to A. swazicum, but occurs on the other side of southern Africa in Namibia and southern Angola. It is an erect shrub with barely succulent stems and only modestly fat roots. The leaves are the largest in the genus. The flowers are nearly circular in outline and are borne from late summer into early winter.. This species shares with A. swazicum petals of uniform pink with no fading toward the darker throat, and the very short anther appendages.
Adenium oleifolium is smaller species, with an underground caudex and a few stems to two feet tall. It comes from the Kalahari Desert of southern Botswana, and northern Namibia and South Africa. It is a slow growing species with relatively small flowers., The branches are densely pubescent when young, becoming glabrous with age. The olive-green leaves are distinctly long and narrow, 50-110 Í 4-13 mm, and are crowded at the tips of the branches. The terminal inflorescence carries a few pinkish salmon or pale pink to red flowers that appear with the leaves.. It is the smallest species in the genus.
Adenium socotranum is rare in the group. It originates only from the isolated island of Socotra in the Indian Ocean south of the Arabian peninsula and east of the Horn of Africa, very near to yeman. This is the giant of the group, with massive trunks up to 15 ft tall and 8 ft in diameter! For many years Socotra hosted a Soviet naval port and was off limits to most everyone, restricting the availability of plants and seeds. In recent years it is accessible, but the authorities are very protective of the natural resources and it is illegal to collect plant material of any type. Adenium socotranum occurs by the thousands in nature, but relatively few plants exist in cultivation. Occasionally seed becomes available from the few plants that are in cultivation. Adenium socotranum is endemic to the island of Socotra (Soqotra).. It differs from all other species (except the Oman form of A. arabicum) in its very short growing season. Plants rarely leaf out before mid summer, and produce stem growth for only a few weeks. The pink flowers appear for a few weeks in spring while the plant is leafless. Its remote location, great size, and until recently unavailability in the trade has made it the holy grail of adeniums. However, it is overrated by collectors, because it is very slow growing and a seedling will take many decades to achieve impressive size in cultivation.