Genera Included: Diogoa Exell & Mendonça, Engomegoma Breteler, Scorodocarpus Becc., Strombosia Blume, Strombosiopsis Engl., and Tetrastylidium Engl.
Habit: Terrestrial, mostly evergreen trees, shrubs.
Parasitism: Scorodocarpus and Strombosia are known to be autotrophic (non-parasitic), thus it is at present assumed that the entire clade is also this trophic condition.
Stem: Twigs glabrous.
Leaves: Phyllotaxy spiral, alternate, or distichous. Leaves without stipules, petiolate with expanded blades, simple, entire, glabrous. Petiole thickened at the distal end (point of attachment to the blade). Secondary venation camptodromous, tertiary venation plagiodromous, quarternary venation (aerolation) meshes polygonal. Leaf unicellular hairs absent, dendritic hairs absent or present. The leaves (and fruits) of Scorodocarpus have a strong odor of garlic.
Leaf anatomy: epidermal cells not lignified; guard cells not lignified, lumina wide, cuticular ledges thick; paracytic and anisocytic stomata absent or present, cyclocytic stomata present; schizogenous cavities in leaf absent; laticiferous channel in leaf absent; druses in epidermal cells absent or present; silicified walls of mesophyll and epidermal cells absent; mesophyll sclereids absent or present; leaf cystoliths absent; petiole and median vein slerenchyma fibers and astroslereids present; vascularization of the nodes trilacunar and pentalacunar; petiole base vascularization a simple vascular cylinder; distal petiole vascularization complex vascular cylinder and one or more adaxial or enclosed strands or a simple vascular cylinder; median vein vascularization complex vascular cylinder and one or more adaxial or enclosed strands or a simple vascular cylinder.
Wood anatomy: vessel grouping solitary or grouped in multiples; perforation plate type simple; vessel member lengths below 900 µm; intervascular pits alternate or opposite; vascular tracheids assoc. w/ vessels absent; fibers as fiber tracheids or libriform fibers; axillary parenchyma abundant; axial parenchyma strands more than 7 cells wide; ray type heterocellular, with several rows of erect or square marginal cells; ray height above or below 1000 µm; wood cystoliths absent; silica bodies in ray cells absent.
Inflorescence: Axillary fascicles composed of cymes or short racemes, sometimes highly contracted (e.g. Diogoa, Strombosiopsis), even to the point of being capitate (Strombosia ceylanica), the flowers arising from a condensed short shoot; bracts present at base of flower (Diogoa) or pedicel and in some cases (e.g. Strombosia glaucescens, S. ceylanica) along the pedicel.
Plant Sex: flowers bisexual.
Flowers: pedicellate or nearly sessile (Diogoa, Strombosiopsis), 4-5
Calyx: cup-shaped, fused at base with short triangular lobes, alternating with petals. Calyx not accrescent (Engomegoma, Scorodocarpus), accrescent (Tetrastylidium), or with an accrescent conceptacle from the transformation of the pedicel/receptacle (Diogoa, Strombosia, Strombosiopsis).
Corolla: appearing fused in bud but apopetalous at anthesis, valvate, with pubescent inner surface (except Strombosiopsis?).
Nectary: glandular disk present, sometimes prominent and lobed (Strombosia), but not accrescent
Androecium: stamens 4-5 (8-10 in Scorodocarpus), adnate to petals, in some genera with an apiculate connective that exceeds the anther locules (Diogoa, Engomegoma, Strombosiopsis, Tetrastylidium); anther attachment basifixed and "dorsi-basifixed"; anther dehiscence introrse or lateral by slits.
Pollen: shape equiaxial; symmetry isopolar or heteropolar; mescolpium flat or convex, apocolpium convex; aperture number 3-4, zonoaperturate; ectoaperture shape elongate, apertural membrane granular or vericose, endoaperture shape circular, ecto- and endoaperture of distinct sizes, endoaperture granules none, endoaperture smooth and present, endoaperture smooth; exine in mesocolpium smooth or with a microperforate tectum and reticulate exine, granules in infratectum absent or present; columella in infratectum absent or present; foot layer surface smooth and irregular with masses.
Gynoecium: ovary superior or becoming inferior during fruit development (Strombosia, Strombosiopsis), 3-5-locular basally and unilocular apically; stigma 3-5-lobed (sometimes minutely).
Ovule: one per locule from a pendulous free-central placenta.
Fruit: ovoid, ellipsoid or spherical drupes. Apex crowned by the persistent style base and/or calyx (Strombosia). In Tetrastylidium the calyx is slightly accrescent around the lower portion of the fruit. In Diogoa, Strombosia and Strombosiopsis, the lower portion of the fruit is embedded in a conceptable (pedicel plus receptacle). The pericarp is generally thin (spongy mesocarp in Diogoa) and the endocarp woody.
Seed: solitary, spherical, with abundant endosperm and a tiny apical embryo.
Chromosomes: Chromosome numbers have been reported from root cells of Strombosia glaucescens var. lucida (Mangenot & Mangenot, 1958): n = 20 (also 40, likely from endopolyploidy).
Alternate family names: Scorodocarpaceae Van Tiegh., Strombosiaceae Van Tiegh., Tetrastylidaceae Van Tieghem.
Link to Family Description (Olacaceae) in Delta