Genera Included: Dulacia Sleumer, Olax L., and Ptychopetalum Benth.
Habit: Terrestrial, evergreen trees and shrubs, rarely lianas.
Parasitism: root hemiparasites, well documented for Olax (see References).
Roots: haustorial. Anatomy of the haustorium of Olax phyllanthii described by Pate et al. (1990).
Stem: without stipules, young branches often zig-zag, longitudinally striate. Stems sometimes 4-sided and winged in Olax, terete in Ptychopetalum.
Leaves: Simple, alternate or alternate-distichous, rarely decussate, glabrous, margin entire. Primary venation pinnate, secondary venation brochidodromous, tertiary venation reticulate, quarternary venation (aerolation) meshes polygonal.
Leaf anatomy: leaf unicellular hairs absent or present; epidermal cells and guard cells not lignified; lumina of guard cells narrow; cuticular ledges of guard cells inconsipuous and thick; paracytic stomata absent or present; cyclocytic and anisocytic stomata absent; schizogenous cavities in leaf absent; laticiferous channel in leaf absent; druses in epidermal cells absent; silicified walls of mesophyll and epidermal cells present; mesophyll sclereids absent; leaf cystoliths absent; petiole and median vein slerenchyma fibers and astroslereids absent; vascularization of the nodes unilacunar or trilacunar; basal and distal petiole vascularization a simple bundle; median vein vascularization a simple bundle.
Wood anatomy: vessel grouping solitary or grouped in multiples; perforation plate type scalariform; vessel member length over 900 µm; intervascular pits alternate; vascular tracheids assoc. w/ vessels present; fiber tracheids and libriform fibers present; axillary parenchyma abundant; axial parenchyma strand width less than 7 cells; ray type heterocellular, one row of erect cells; ray height short, below 1000 µm; wood cystoliths absent; silica bodies in ray cells present.
Inflorescence: axillary, cymose racemes, axis zig-zag (Dulacia, Olax); pedicels subtended by caducous bracts that are usually small but sometimes persist and become foliose.
Plant Sex: flowers generally bisexual (rarely unisexual in Olax).
Flowers: buds oval in shape; flowers 5-6 merous.
Fruit: drupes, surrounded by accrescent calyx in Dulacia and some Olax; endocarp coriaceous or crustaceous.
Seed: with copious oily endosperm, also starch present (Dulacia); embryo tiny.
Chromosomes: Chromosome numbers have been reported for Olax nana (Khosla, 1978; Mehra, 1976): n = 12, 24 and Olax hypoleuca (Carr & McPherson, 1986) with the same numbers.
Alternate Family Names: none.