Citrullus lanatus (Thunb.) Matsum. & Nakai var. lanatus, watermelon, sandia. Annual vine, trailing, tendril–bearing, taprooted, several–stemmed at base, prostrate on ground with principal shoots diverging from base; monoecious; shoots long and often unbranched or sparsely branched, with only cauline leaves, somewhat scabrous, pubescent with some stiff, long, unbranched hairs to 5 mm long and shorter nonglandular hairs with broad bases; tendril 1 per node, arising to 1 side of petiole base ⊥ to stem, to 50 mm long, 2–forked below midpoint, the stalk to 30 mm long, conspicuously long–hairy, the branches low–ridged, strongly coiled under several times, pale green, flattish on upper side and rounded at tip, glabrous along most of length.
Stems5–sided with rounded edges, to 5 mm diameter, with each ridge descending from each leaf, tough.
Leaves helically alternate, deeply pinnately lobed, blades ± symmetric with mostly 3 opposite (subopposite) pairs of lobes and the lowest pair often sublobed, petiolate, without stipules; petiole ± cylindric, to 55 mm long, tough, pubescent like stem; blade ovate in outline < 40—155 × < 30—130 mm, lobes decreasing base to top, often mitten–shaped and subentire to low–crenate but teeth poorly defined except at callus on margins, sinuses mostly < 5 mm from midrib and roundish, lateral lobes asymmetric, to 60 × 60 mm, terminal lobe ± obovate and symmetric, to 55 × 35 mm, pinnately veined having 3 veins at base (2 into basal lobes) with principal veins mostly raised on upper surface and conspicuously raised on lower surface, surfaces with long hairs along principal ceins and shorter hairs on green tissue.
Inflorescence flowers solitary, axillary, unisexual, staminate flowers in a population often more common than pistillate flowers, lacking bracts, pubescent; pedicel curved to orient flower upward, petiolelike, of staminate flower at anthesis ca. 12 mm long and abscising at base, of pistillate flower at anthesis twisted and ca. 10 mm long increasing to 50 mm long in fruit, densely long–hairy.
Staminate flower radial, ca. 25 mm across, densely hairy; hypanthium dishlike below calyx, ± 3.5 mm long, spotted green, with long hairs; sepals 5, arising from hypanthium, free or barely united, ± linear, 5.5 × 0.8 mm, green, short–hairy; corolla 5–lobed, arising from hypanthium, dishlike; tube about 2 mm long; lobes obovate, ca. 11 × 7 mm, light yellow with green veins, with ca. 7 parallel veins at base, rounded at tip, short–hairy with long hairs on lower surface along raised veins; stamens 3, fused to base of corolla tube; filaments erect, thick and ridged, 3.5—4 mm long, greenish yellow, with some short hairs; anthers oriented outward, basifixed, dithecal and contorted, 4 × 5 mm, light yellow–orange, longitudinally and outwardly dehiscent; pollen yellow; pistil vestigial, broadly inversely conic, 1 × 2 mm.
Pistillate flower radial, ca. 20 mm; hypanthium saucerlike, ± 2.5 mm long, spotted green like ovary, with long hairs; sepals 5, arising from hypanthium, free or barely united, appressed, ± linear, 5.5 × 0.8 mm, green, short–hairy; corolla 5–lobed, arising from hypanthium, dishlike and fused only at base; lobes obovate, ca. 10 × 8 mm, light yellow with green veins, with 5 or 7 parallel veins at base, rounded at tip, short–hairy with long hairs on lower surface along raised veins; stamens 3, vestigial staminodes, fused to corolla tube, truncate, ca. 1.2 mm long, pale green; pistil 1; ovary conspicuously inferior (even in small bud), oblanceoloid, at anthesis ca. 10 × 5 mm, green with rows of lighter spots in longitudinal stripes, densely long–hairy, 3–chambered with many ovules attached to outer wall, constricted at top with narrow 2 mm tube beneath hypanthium; style 3–branched above midpoint, ca. 3 mm long, green, glabrous; stigmas 3, spreading, ca. 5 mm across, each appearing 2–lobed and ± heart–shaped, 2.5 × 2.5 × 0.8 mm, fleshy, glossy yellow, densely papillate–glandular, sticky.
Fruit pepo (= indehiscent berry with firm, breakable outer shell), many–seeded, oblong–ellipsoid, in range (observed) 250+ × 150+ mm, dark green large green blotches arranged in rows, glabrescent; pulp firm, sweet, juicy, red.
Seed (mature seeds not observed in range) compressed–ovoid, black, flat and slightly convex on surfaces.
A. C. Gibson