Everyone can spot a watermelon fruit, but fewer people know what the vine and its leaves look like when they visit a spacious vegetable garden. Native to Africa, watermelon (Citrullus lanatus) quickly sprouts, grows, flowers and set fruits within one growing season, making it an annual vine. Plant it in sunny, moist but well-draining soils when no frosts occur. Seeded and seedless types of watermelons all look the same until you slice open the juicy fruits.
Look at the stems of the plant. Watermelon's hairy stems grow long and sprawl across the soil or ramble atop nearby shrubbery. They grow as long as 20 to 30 feet in length and look for curly tendrils emanating from the stem tips.
Note the foliage. Though similar to those of a pumpkin, squash or cucumber, a watermelon plant's leaves grow no larger than an adult's hand. Look for leaves that are medium to light green with ornate lobes. Each leaf has a hairy surface and three to five lobes with possible rounded teeth on each lobe. Even newly germinating watermelon plants quickly develop leaves with these lobes, helping identify plants even before the long stems develop.
Examine the flowers, if necessary, noting their light green-yellow color and the fused, five petals. Each blossom contains both sex organs: the female pistil and the male stamens that bear pollen. According to the University of Delaware College of Agriculture, the flowers open an hour or two after sunrise each day.
Look for fruits. Even small, immature fruits have thick, smooth and waxy skin. When small, they typically remain solid green but then develop stripes or mottled blotches of various green tones. Some varieties mature with dark green skin.