Watermelon, cucumber and gourd are members of the plant family Cucurbitaceae, which consists of crops commonly referred to as cucurbits. While each plant is classified as a different species and is a member of a different genus, they are all related. Watermelon, cucumber, gourds and other members of the cucurbitaceae family share similar growing and care requirements, and have similar physical characteristics as well.

The Family Cucurbitaceae The Cucurbitaceae plant family, also referred to as cucurbits, comprises about 100 genera and 700 species of vining plants, including cucumbers, watermelons, gourds, pumpkins, muskmelons and squash. Cucurbitaceae plants are similar in appearance and growth requirements. For example, all crops in this family are sprawling vines that typically have tendrils, and the flowers are bright yellow on all cucurbits except for the bottle gourd. Each plant in this family forms both male and female flowers. While the edible parts of plants in the cucurbitaceae family are often referred to as vegetables, they are actually fruit. The relationship between these crops has made home gardeners wary of planting them together, because some people believe that they cross-pollinate. However, cross-pollination is possible only between members of the same species; so watermelon, cucumbers and gourds can grow in the same garden without cross-pollination occurring.

Watermelons Watermelon (Citrullus lanatus) is part of the genus Citrullus. This genus contains four species of plants, including watermelon and Citrullus colocynthis, also known as bitter apple, Citrullus ecirrhosus, also known as wild melon, and Citrullus rehmii, a South African species of wild melon. Watermelon is sometimes referred to as Citrullus vulgaris, but the species descriptor "vulgaris" refers to the same plant and means "common." Watermelons need a long growing season of 70 to 90 days, with daytime temperatures around 80 degrees Fahrenheit. They are hardy in U.S. Department of Agriculture plant hardiness zones 3 through 11, and both seeded and unseeded varieties are available. Although still considered a type of melon, watermelons are not part of the melon genus Cucumis. They're categorized as a separate species of melon.

Cucumbers Cucumbers (Cucumis sativus) are warm-season crops that are hardy in USDA zones 4 through 11. Cucumbers are great climbers, so they can be grown in relatively small garden spaces if given a strong support to climb. These cucurbits do best when average daytime temperatures are around 70 degrees F, and they require between 55 and 65 days to mature. Once the fruit of a cucumber plant begins to ripen, you can typically harvest them for several weeks.

Gourds Gourds may be part of one of two genera: Cucurbita and Lagenaria. Those in the genus Cucurbita are colorful and grow in a range of shapes, including apple-, pear- or bell-shaped. These gourds may be smooth-skinned or warty, plain or solid-colored, ridged or striped. Lagenaria genus gourds are sometimes referred to as bottle or dipper gourds. These may also be smooth, knobby or ridged and vary in size, with some as small as 3 inches long and others more than 3 feet long. Shapes in this gourd genus include globe, bottle, dumbbell, crookneck and coiled. Gourds thrive in temperatures between 70 and 85 degrees F and have a long growing season of about 100 to 180 days, depending on the variety.

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