Octoknemaceae Soler.

Genera Included:  Octoknema Pierre.

Habit: Terrestrial, evergreen trees or shrubs. Octoknema orientalis is a tree reaching 40 m whereas O. affinis is a low-branching tree up to 20 m or a 2-6 m shrub.   

Parasitism: trophic condition has not been established. The position of Octoknema on the molecular tree in MalÚcot and Nickrent (2008) suggests it is parasitic.

Roots: no information.

Stem: For O. affinis, Louis and Leonard (1948) say "trunk cylindrical, deprived of basal buttresses, being able to reach 50 cm of diam; dense summit; scaly rhytidome, gray beige or ashy gray; bark 3-8 mm thick, yellowish on fresh section, somewhat tender, nonfibrous; young parts (branchlets, petioles and inflorescences) densely covered with stellate hairs." For O. orientalis, "the slash is soft and yellow with a clear exudate near the wood.  The bark is pale brown, flaking in patches" (information from herbarium label on specimen collected by Lovett, Langson and Kisona no. 57956 from Tanzania, at Kew).

Leaves: Alternate, simple, petiolate, estipulate. Primary venation pinnate, secondary venation camptodromous, tertiary venation plagiodromous, quarternary venation (aerolation) meshes polygonal.  Leaves of O. affinis described a glabrous with a shiny, yellow-green upper surface and prominent venation on the lower surface.  For O. orientalis (Lovett et al. 57956) "young leaves red with green veins and distinctive stellate hairs." In Lucas (1968) the young leaves are described as prominently stellate pubescent towards petiole on underside, secondary veins prominent beneath, impressed on upper surface, tertiary veins reticulate and more or less prominent on both surfaces.

Leaf anatomy: leaf unicellular hairs absent; epidermal cells and guard cells not lignifed; lumina of guard cells narrow; cuticular ledges of guard cells thick; paracytic and cyclocytic stomata absent; anisocytic stomata present; schizogenous cavities in leaf absent; laticiferous channel in leaf absent;  druses in epidermal cells absent; silicified walls of mesophyll and epidermal cells absent; mesophyll sclereids absent;  leaf cystoliths absent; petiole and median vein sclerenchyma fibers and astroslereids present; vascularization of the nodes pentalacunar or more; basal, distal, and petiole median vein vascularization a simple vascular cylinder.

Wood anatomy: vessel grouping solitary; perforation plate type scalariform; vessel member length below 900 Ám; intervascular pits (if present) opposite;  vascular tracheids assoc. w/ vessels absent; fibers as libriform fibers; axillary parenchyma frequency rare or absent; axial parenchyma strand width more than 7 cells; ray type heterocellular, several rows of erect or square marginal cells; ray height long, over 1000 Ám; wood cystoliths absent; silica bodies in ray cells absent.

Inflorescence: The description (translated to English) in Louis and Leonard (1948) for O. affinis is "inflorescences generally axillary, male in the form of fascicled spikes 1- or few-flowered, female in the form of simple and few-flowered spikes." But the illustrations and text show that the male flowers have pedicels, thus this inflorescence should be referred to as a raceme. The illustration and text agree on that the female inflorescence is a spike.  For O. orientalis, Lucas (1968) describes the female inflorescence as a spike, with sessile flowers and this agrees with the illustration; in the generic description "inflorescence axillary, racemose".  Male inflorescences were unknown here.  However, the Lovett et al. (57956) specimen of O. orientalis is male and on its inflorescences the flowers are pedicellate.  These inflorescences tear through the branch epidermis making their origin endogenous. They appear as contracted racemes or fascicles.  Thus it appears that in both species, the male inflorescence is a raceme whereas the female one is a spike.

Plant Sex: dioecious.

Flowers: unisexual, with remnants of the other essential floral whorls present (staminodes and pistillodes); 5-merous.

Fruit: an ellipsoidal to spherical drupe crowned by the persistent petals, external surface covered with stellate trichomes; ectocarp, mesocarp and endocarp present, the latter with 6-10 thin blade-like intrusions into furrows of the seed.

Seed: with longitudinal furrows (formed with the intrusive endocarp); endosperm with oil and starch.

Chromosomes: no chromosome numbers reported.

Alternate Family Names: Octoknema has been included in Olacaceae.  Moreover, Octoknemaceae was considered to include Okoubaka (see Louis and Leonard 1948) which is now placed in Cervantesiaceae (a segregate of Santalaceae).

Last updated: 14-May-18 / dln