Sapindus oahuensis is a tree that can reach heights of 6 to 15 meters, with gray, textured, and rough bark adorned with lenticels. The youngest branches exhibit a yellowish-brown tomentose covering. The leaves are simple, alternate leaves with blades ranging from ovate to elliptic or oblong-ovate, measuring 7.5–27 cm long and 3–14.5 cm wide. The leaflets are arranged sub-oppositely or alternately. They possess an acute apex and a base that ranges from rounded to truncate, often showing a unique inequilateral decurrent form. The leaf surfaces are glabrous and green with a conspicuous yellow midrib. Although the leaf material is thick-chartaceous, the margins are entirely and typically slightly undulate. The petioles are notably 0.8–10 cm long and are swollen at the base. No stipules are present. The flowers emerge in axillary panicles that span 5–35 cm long. Exhibiting a monoecious nature, the plant has unisexual, actinomorphic (radially symmetric) flowers. These flowers are supported by 2–5 mm long pedicels and pubescent. The calyx consists of 5 sepals that are broadly imbricate and unequal in size, with the outer sepals being ovate and the inner ones being suborbicular and densely pubescent. The corolla features five equal, narrowly ovate petals, each about 3 mm long, pubescent on the outer surface and edges, and each with a 2-lobed, pilose scale at the base on the inner surface. It has eight stamens with pubescent filaments in the lower half, inserted on a 5-angled nectary disk. The anthers are ellipsoid, introrse, dithecal, and open via longitudinal slits. Staminate flowers have a rudimentary ovary, while pistillate flowers feature a fully developed, ovoid, glabrous, 2–3-celled ovary with a terminal style and a 3-lobed stigma. The fruits comprise 1(2) fleshy, obovoid mericarps, each 2–3 cm long, with a glossy, leathery pericarp. Each mericarp houses a single, obovoid seed, 15–18 mm long, and has a black, rugose seed coat with a truncate base. These seeds lack endosperm. It occurs in mesic to dry forests between 60-610 meters.
Bean-shaped (Reniform): Resembling the shape of a kidney or bean.
Square or Oblong: Angular shape with all sides more or less equal or longer than wide.
Triangular: Three-sided shape, broadest below the middle.
Elliptic: Rounded at both ends. shaped like an ellipse or oval.
Ovate or Obovate: egg-shaped, broader at one end.
Linear: Extremely long and narrow, with sides usually parallel.
Round: Appears circular, with length and width roughly the same.
Cardioid (Heart-Shaped): One edge has a prominent double curve into two lobes.
Cylindrical: A cylinder with parallel sides and a circular cross-section.
Discoid: Resembling a disc or plate with two relatively flat surfaces.
Fusiform: Spindle-shaped, tapering at both ends.
Globose: Spherical.
Lenticular: Resembling a lens with two convex surfaces.
Ovoid: Egg-shaped.
Plano-convex: Having a flat ventral (planar) surface and a curved dorsal (convex) surface.
Polygonal: Having more than three flat faces meeting at angles.
Sectoroid: Resembling a segment of an orange with two relatively flat faces and one curved face.
Subglobose/ellipsoid: Inflated shape but less than spherical.
Trigonous: Having three faces that meet at a distinct angle; triangular in cross-section.
Endangered species (E) are species that are so rare they’re in danger of becoming extinct.
Threatened species (T) are species that are likely to become endangered within the foreseeable future throughout all or a significant portion of their range.
Species of Concern (SOC) are species about which there are some concerns regarding status and threats, but insufficient information is available to list the species under the Endangered Species Act (ESA).
Plant Extinction Prevention (PEP) is a state status for rare plants that focuses its efforts on species that have fewer than 50 remaining wild individuals.
Orthodox seeds (desiccation-tolerant): can be dried to an internal seed moisture of less than 12% water and stored at freezing temperatures.
Intermediate seeds (temperature-sensitive) tend to age faster than orthodox seeds and may have only a 5-year lifespan when stored at -20°C. They are recommended for storage at 5°C.
Recalcitrant seeds (desiccation-sensitive): cannot be stored in a conventional freezer as they cannot survive after drying and/or freezing at -20°C. They are recommended for cryopreservation storage.