The watermelon plant, scientifically known as Citrullus lanatus, is a warm-weather annual that produces one of the most recognizable fruits. It belongs to the large botanical family Cucurbitaceae, which also includes squashes, cucumbers, and gourds.
Overall Growth Habit and Vine Structure
Watermelon plants are characterized by their prostrate growth habit, meaning they sprawl extensively along the soil surface. Seedlings initially emerge with two small, oval cotyledons before developing their first true leaves.
As the plant matures, a central primary vine develops, which can stretch significantly, typically ranging from 6 to 15 feet in length. Multiple secondary vines branch off from this main stem, contributing to the plant’s wide spread.
The vines are generally cylindrical and somewhat ribbed. Nodes, where leaves and tendrils originate, occur regularly along the length of both the primary and secondary stems.
Distinguishing Features of Leaves and Stems
The leaves of the watermelon plant are perhaps its most distinct vegetative feature, easily setting it apart from many other garden plants. They are large, deep green, and possess a deeply lobed or palmate structure, often described as deeply incised. Each leaf blade typically features three to seven distinct lobes, giving the leaf a highly dissected appearance.
A defining characteristic of both the leaves and the stems is the presence of fine, stiff hairs, a trait known as pubescence. This dense covering gives the entire plant a rough, textured feel. This layer of hairs plays a role in reducing water loss and protecting the plant surface.
The stems themselves are robust and slightly angled or ribbed, carrying the same fuzzy texture as the leaves. Unlike some related cucurbits, watermelon stems are not smooth but maintain this characteristic roughness throughout their length.
Emerging from the nodes opposite the leaves are tendrils. These are slender, unbranched coils that wrap tightly around nearby objects, providing anchoring and stability to the sprawling vine. These tendrils allow the plant to secure itself to the ground or low supports, preventing the long vines from being easily displaced by wind or movement.
Appearance of Flowers and Developing Fruit
Watermelon plants are monoecious, meaning individual plants produce separate male and female flowers. Both flower types are typically bright yellow, possessing five petals that open widely to attract pollinators. The overall size of the flowers is modest, generally measuring between one and two inches in diameter.
Male flowers usually appear first and are significantly more numerous than the female flowers throughout the growing season. They are easily identified by the long, slender pedicel, or flower stem, that supports them. Once their pollen is shed, these male flowers wither and fall off the vine.
Female flowers are distinct because they have a small, bulbous swelling directly beneath the yellow petals, which is the nascent ovary, or unfertilized fruit. This swelling is a visibly miniature version of the fruit, differentiating the female flower from the male, which lacks this structure. Female flowers are supported by a much shorter, stouter pedicel.
Successful pollination transfers pollen from the male flower to the stigma of the female flower, initiating fruit development. Immediately after the petals drop, the small, fuzzy ovary begins to rapidly increase in size. At this early stage, the developing fruit is typically a matte green and still covered in the fine pubescence characteristic of the rest of the vine.