The Free Dictionary defines Cucurbita maxima as a plant with grey-green or buff-colored fruit. These fruits are commonly called winter squash and include the common butternut squash and hubbard squash. Some Cucurbita maxima varieties have thin, smooth rinds and some have rough, warty rinds. Most Cucurbita maxima varieties have a fine-textured interior.
Cucurbita mixta is a plant with a striped and warty rind. These fruits are usually ovoid or globose and contain the cushaw--or curved long-necked--squash varieties. The coloring of Cucurbita mixta varies from grey to green to white stripes.
Cucurbita moschata is defined as any squash with a hard rind and a cushaw-styled curved long neck. These fruits are frequently called winter squash and include the winter crookneck squash. Cucurbita moschata are commonly two-color combinations of green, yellow, orange and white.
Cucurbita pepo is a vine widely cultivated for a round orange fruit with a firm rind and numerous seeds. These fruits are frequently called pumpkins and include the autumn pumpkin variety. Cucurbita pepo is commonly used each Halloween in many cultures to create jack-o-lanterns, traditional Halloween decorations featuring facial features carved in the hollowed fruit rind and lit from within by a candle.
According to K.S. Delaplane and D.F. Mayer of the University of Delaware, some interspecies cross-pollination is possible with members of the Cucurbita L. genus. Cucurbita maxima will not cross-pollinate. Cucurbita mixta will cross-pollinate with Cucurbita moschata. Cucurbita moschata will cross-pollinate with Cucurbita mixta. Cucurbita pepo will cross-pollinate with Cucurbita moschata. Many variations of traditional gourd species may arise from these available cross-pollinations.