Notes on the genus Cussonia in South Africa

Information gathered during studies of the genus Cussonia under field conditions is presented. The development of the inflorescences, and branch and leaf initiation, is given special attention. The subdivision of the genus  Cussonia is discussed and the following new subgeneric taxa are created: Subgenus  Cussonia (type species: C.  spicata  Thunb.) with two sections: Sect.  Cussonia and Sect. Capitata  Strey; Subgenus  Paniculata  Strey (type species: C.  paniculata Eckl. & Zeyh.); Subgenus Protocussonia  (type species: C.  natalensis Sond.). It is pointed out that the names C. kraussii Hochst. and C .  chartacea Schinz have been misapplied to two undescribed species, and are synonyms of C. spicata Thunb. and  Schefflera umbellifera  (Sond.) Baill., respectively. Four new species are described viz. C. arenicola Strey, C. zuluensis Strey, C . nicholsonii Strey and C . sphaerocephala Strey.

In the course o f studies o f the genus Cussonia a number o f interesting facts emerged, especially from the field studies that were undertaken. Several o f these features, particularly the development o f the inflorescence, the m ode o f flow ering and the renewal o f vegetative grow th after flowering, have apparently not been recorded before and are therefore discussed in the follow in g pages. It was also discovered that two names had been misapplied and that the species masquerading under these names were new and required to be described. In addition, tw o new species were identified and are described here. I am indebted to D r D. J. B. K illick fo r the Latin descriptions.
The majority o f specimens studied are deposited in the National Herbarium , Pretoria, and N atal H er barium, Durban. Those seen in other herbaria are specially indicated.

The development o f the inflorescence
In all species o f Cussonia the structures bearing the flowers are borne in clusters at the apices o f branches or in some cases even at the apices o f fairly thick trunks. These clusters usually consist o f a few to many peduncled spikes, racemes or even panicles originating in the axils o f the apical bracts which are numerous and in dormant branches com pletely cover the apices. A t the beginning o f a new season when the trees start sprouting it is soon evident that branch apices either produce a new flush o f leaves or somewhat m ore slowly develop inflorescen ces. Leaves and inflorescences are seldom, i f ever, simultaneously produced at the apex o f the same branch. Whereas branches producing inflorescences may be leafy, these leaves are alm ost invariably produced during the previous season and are usually shed before the inflorescences are mature. Mature and particularly fruiting inflorescences are therefore borne at the apices o f bare branches. In all the species studied, the clusters o f pedunculate flower-bearing branches together form an apical compound in florescence, since no normal leaves are produced ' Botanical Research Unit, Botanic Gardens Road, Durban. by the bract-covered apices from which the inflorescence-branches develop. The development o f the inflorescence o f two o f the species studied differs fundamentally from the pattern displayed by the others. In most species the inflorescence bud initials are laid down in the bract-covered apices o f some o f the branches towards the end o f the grow ing season and develop from these usually in the follow in g spring. The situation in Cussonia spicata and C. sphaerocephala is quite different. Instead o f producing inflorescences, an " umbel" o f fairly slender leafy branches is produced at the apex o f a trunk during the first season. Each branch has a knob-like thick ening covered with bracts, at the apex. Only during the follow in g season are inflorescences produced at the apices o f these branches. Since the leafy branches form ed during the first season lose their year-old leaves, as soon as the inflorescences start developing, the final structure resembles a compound " umbel" at the end o f the second season. These pseudo inflorescences are therefore biennial structures in contrast to the inflorescences produced by other species which develop in one year.

The flowers and fruits
The fully-developed flowerbuds open up in irregular sequence on almost any parts o f the spikes or racemes, at the base or the apex or at the middle, and in addition one side o f the spike may be in full flower when no flowers have opened on the other side. Flowers at various stages o f development are there fore found irregularly grouped in the inflorescences. The open flowers are star-shaped with the petals and stamens stiffly spreading. The petals and stamens are very easily detached and are never preserved in situ in dried specimens. N e w ly opened flowers are greenish-cream to butter-yellow in colour, the top o f the ovary green, the stigmas pale and erect and the anthers yellow. A s the flow er ages the petals and stamens drop, the top o f the ovary becomes yellow and exudes a shiny, sticky fluid which attracts insects, the stigmas become darker and the styles recurve. It is probably at this stage that pollination is effected by the various types o f insects found on the flowers, including bees, flies and beetles. N o t all ovaries are fertilized. The ones that are fertile increase in size and develop a fleshy purple exocarp attractive to birds. Each fruit con tains one to two seeds. Unfertilized and parasitized ovaries may develop but remain dry and hollow structures. Mature inflorescences are attacked by insects and the stem-apex in particular seems sus ceptible. When the stem-apex has decayed, the whole inflorescence breaks o ff and drops to the ground.

The formation o f new branches
The apices o f the stems which have fruited and have subsequently lost the inflorescences, are now usually more or less truncate and dry out, or develop a certain amount o f callus-tissue. These truncated branches and trunks eventually produce side-shoots which continue the growth o f the branch. It appears that side-shoots are seldom form ed on actively growing vegetative branches and trunks in the sparingly branched species such as C. spicata and C. sphaerocephala, but that usually one, rarely more, sidebranches are form ed after the growth o f a trunk or branch has been temporarily halted by production o f an inflorescence or by injury. In species which by nature have a more branched habit, such as C. natalensis, several shoots originate from dormant buds after the inflorescences have been discarded.

Leaf-form and development
The leaves, which in all species are clustered at the ends o f branches, are, in most species, produced in flushes. The young leaves mature and usually remain on the tree fo r a full year. Old leaves lower on the stems are gradually cast o ff after a new flush o f leaves has appeared so that the clusters are always situated apically. Usually only one flush o f leaves per year is produced. Renewal o f leaves, as also the production o f inflorescences, is not only seasonally determined and may vary from tree to tree.
In shape the leaves vary from simple and deeply lobed to singly or doubly compound.

V ER T EBR A T E LEAFLET
most elaborate development. The vertebrate leaflets have 1-5 articulations, characterized by turgid green papillate scales on the lower suface. These scales may represent reduced bracts. A t these articulations the pinnules are attached. The articulations may be devoid o f pinnules, o r bear two, four or six pinnules arranged in a whorl, the numbers increasing pro gressively upwards. The terminal pinnules o f the vertebrae usually repeat the form o f the lowest leaflet, i f this is a simple structure. Because o f the size o f the compound leaves, only single leaflets are usually represented in herbaria and the leaf-structure is usually not fully understood. In Fig. 1 a complete leaf o f C. spicata is semi-diagrammatically represented.
This figure also serves as a reference to the term inology used in this paper.

Bark, wood and roots
The w ood is soft, light, very coarse and fibrous and the branches have a distinct pith. The bark o f most species is thick and corky and usually fissured, but it is thinner and less corky and more smooth in forest trees. The roots o f all species investigated are thick, fleshy and frequently tuberous. Depending on the species the roots may form a single large tuber, may be thick and fleshy or produce a series o f tuberous swellings along their length. Such roots are often used as a source o f water by animals and also by man.

C L A S S IF IC A T IO N A N D S U B D IV IS IO N S O F T H E G E N U S C U S S O N IA
The family Araliaceae to which Cussonia belongs is represented in South A frica by three genera. spicata is C. sphaerocephala Strey which is newly described in this paper. Therefore these two species represent typical Cussonia.
The development o f the inflorescences in the latter two species is described in detail earlier in this paper and distinguishes them from the follow in g species which, in other respects are closely related to them, namely, C. thyrsiflora Thunb., C. arenicola Strey, C. nicholsonii Strey and C. zuluensis Strey. A ll the previously mentioned species have the follow ing characteristics in com m on: they bear fairly large pedunculate spikes or racemes in terminal compound inflorescences on relatively sparsely branched plants; their leaves are m ostly doubly compound and the leaflets o f the vertebrate type, except fo r C. thyrsiflora which usually has simple leaflets.
A second distinct group is represented by only one species, namely, C. paniculata Eckl. & Zeyh.
which may be distinguished from all other species by the paniculate branches o f the inflorescence and the elongate simple, shallowly to deeply lobed leaflets which are never vertebrate.
The third group is composed o f species which have palmatifid. palmatisect or digitately com pound leaves. There seems to be a somewhat gradual transition from palm atilobed-palmatifid-palm ati sect-digitately compound leaves (see also Aitken. 1923, p. 58), and a further division o f the species into tw o groups, one possessing simple lobed leaves (e.g. C. natalensis) and a group possessing compound palmatisect or digitate leaves was contemplated but abandoned.
Th e follow in g subgenera and sections are described to accom m odate the South African species o f the genus. It seems likely that most o f the tropical species can, without much difficulty, be accommodated in these subdivisions. Species included: C. spicata Thunb., C. sphaero cephala Strey.
This subgenus is monotypic.

M IS A P P L IE D N A M E S
During the investigation it was found that two names o f long standing were misapplied and should be relegated to synonymy. The specimens to which these two names were applied, represent three distinct undescribed species. Single-stemmed shrubs, 1-2 m high; stems 1-2 cm thick, arising singly from a globose, ovoid or turbinate tuber; basal tubers up to 14 cm broad and up to 25 cm long often several spaced along a single root; bark smooth greenish or grey. Leaves glabrous or with scattered scale-like papillae at the articulations, twice compound, first division digitate, bearing vertebrate leaflets; petiole ribbed, terete, up to 25 cm long, 2-4 mm thick; stipules intrapetiolar, joined at the base, adnate to the base o f the petiole, lobes 2-3 mm long; limb o f the lea f sub-circular in outline, about 20 cm in diam .; leaflets 4-7(12) per leaf, 6-18 cm long, chartaceous, dark green above, dull green beneath, margin revolute, serrate, 1-3 times vertebrate, petiolules about 1(2) cm long, usually narrowly winged, rhachilla wings obtriangular to obhastate; pinnules up to 9 cm long and 2-4 cm wide, sessile, 1-5, obovate-oblanceolate, or trullate, base cuneate, rounded, acute or apiculate. A species mainly found on the coastal sand-dunes o f northern Natal but occasionally further inland in sand forest (Fig. 3). The specific epithet arenicola meaning " dwelling on sand" was applied to this species, because it is the only species which is confined to sandy habitats. Small trees with several stems, up to 4 m high, trunks 2-5 cm thick, rarely branched; w oo d coarse, long-fibrous, pithed; bark smooth, flaking, greygreen; roots tuberous, with fleshy fusiform swellings.
A species found in the coastal areas from Durban to Mozam bique (Fig. 5). It inhabits dry scrub and open dry forest, often found in the river valleys and occurs in the thornveld as far inland as Weenen in Natal. Specimens from riverine bush have larger leaves which are less divided and greener. C. zuluensis is usually easily distinguished from all other South African species o f Cussonia by the length of the pedicels o f the flowers and fruits which are seldom much less than 1 cm in length and usually much longer. From C. thyrsiflora it may be distin guished by the leaves which have (3)5-7(8) leaflets which are once or twice vertebrate in contrast to the usually 4-5 simple (or rarely once vertebrate) leaflets of C. thyrsiflora. Whereas this species is a small tree with several erect stems, C. thyrsiflora is a scandent scrambler with m ore or less patent branches.
From C. nicholsonii it differs by the pedicellate (not sessile) flowers, the less dense inflorescence and the shape o f the fruits which have a rounded, not cuneate base.
Differs from C. arenicola by the cluster o f tubers producing a number o f stems set closely together and by the differently shaped fruits, those o f C. zuluensis being goblet-shaped an 1 vertically grooved between the locules.
The name is derived from the area to which it is mainly confined, namely Zululand in northern Natal.
A species found mainly in the coastal areas o f Natal (Fig. 7). It inhabits a fairly wide range o f ecological habitats from hillsides to Euphorbia scrub and riverine bush.  This species occurs from Port St. Johns to Kosi Bay in coastal dune forest, but is also com m on in moist frost-free high forest kloofs up to an altitude o f 1 300 m preferring south-eastern aspects, crowns often emerging from the surrounding canopy and very conspicuous (F ig . 9). N ot yet recorded outside o f the Transkei and Natal.
3 3a 3b •4 4a 5 6 0 A A 12 13 14 14a F i g . 8.-1, Cussonia sphaerocephala, habit; 2, pseudoinflorescence X 1/20; 3, 3a, seed, front and back view; 3b, surface o f seed enlarged x 5; 4, 4a, petal front and side view X 1^; 5, stamen X 1J; 6, anther x 5; 7, flower bud x l i ; 8, flower at anthesis; 9, longitudinal section o f flower at anthesis x I i ; 10, longitudinal section o f mature flower x 1^; 11, buds showing arrangement in spike X J; 12, flower viewed from above x J; 13, arrangement o f bracts and bracteoles X 1|; 14-14b, bracts, front view X 1j.  C. sphaerocephala has been erroneously referred to as C. charlacea by several authors and this is the name it generally bears in herbaria. A s explained earlier in this paper under " Misapplied Nam es" , C. chartacea Schinz is a synonym o f Schefflera untbellifera (Sond.) Baill. The habit and habitat o f this species are described by Aitken (1923, p. 59), who relates it to C. spicaia Thunb. In spite o f mentioning the possibility that it could be a distinct species, he favoured the view that it was an ecological form o f C. spicata occurring on " slopes with southern exposure covered with close bush" . H e was apparently not aware o f the form o f C. spicaia which occurs in forests, since he described the habitat o f the latter as " tree-veld on hillsides with northern exposure". The specific epithet was chosen to describe the striking spherical, terminal leaf-clusters, which characterize the species.