C. maxima - hubbard squash, buttercup squash
C. mixta - cushaw squash
C. moschata - butternut squash
C. pepo - most pumpkins, acorn squash, summer squash

 References:

ITIS 22365 2002-11-06
Hortus Third Squashes are four species of the genus Cucurbita, also called pumpkins and marrows depending on variety or the nationality of the speaker. Squashes are categorized as summer squash or winter squash, depending on when they are harvested. Compare Gourds.

Summer squashes, including young vegetable marrows (such as zucchini [also known as courgette], pattypan and yellow crookneck) are harvested during the summer, while the skin is still tender and the fruit relatively small. They are consumed almost immediately and require little or no cooking.

Winter squashes (such as hubbard , Buttercup squash , acorn, vegetable spaghetti and pumpkin) are harvested at the end of summer, generally cured to further harden the skin, and stored in a cool place for eating later. They generally require longer cooking time than summer squashes. (Note: Although the term winter squash is used here to differentiate from summer squash, it is also commonly used to mean only those of the maxima species.)

Squash is native to North America and was one of the "Three Sisters" planted by Native Americans. The Three Sisters were the three main indigenous plants used for agriculture: maize (corn), beans, and squash. These were usually planted together, with the cornstalk providing support for the climbing beans, and shade for the squash. The squash vines provided groundcover to limit weeds.

Besides the fruits, squash seeds, blossoms, and tendrils are also edible. The blossoms are an important part of native american cooking and are also used in many other parts of the world.

Pollination

Squash has historically been pollinated by the native North American squash bee Peponapis pruinosa, but this bee has declined, probably due to pesticide sensitivity, and most commercial plantings are pollinated by honeybees today. One hive per acre (4,000 m² per hive) is recommended by the US Department of Agriculture. Gardeners with a shortage of bees often have to hand pollinate . Inadequately pollinated squash usually start growing but abort before full development. Often there is an opportunistic fungus that the gardener blames for the abortion, but the fix proves to be better pollination not fungicide.

Squash species

Four species of the genus Cucurbita are called squash or pumpkins rather indiscriminately.

• C. maxima includes the large winter squashes (such as Hubbard and Banana) and some large pumpkins, and numerous smaller varieties such as Buttercup and Mooregold. On this species the peduncle (fruit stem) is spongy and swollen, not ridged.
• C. pepo includes the small pie pumpkins, standard field pumpkins, acorn squash, vegetable spaghetti, zucchini, summer crookneck squash, pattypan and most other summer squashes.
• C. moschata includes butternut and cheese squashes, among others
• C. mixta includes the cushaw varieties.

While squashes and pumpkins are notorious for producing hybrids when grown together, the different species do not usually hybridize with each other.

Squash Images

Petit Pan squash

Longtitudinal section of female flower of squash (courgette), showing ovary, ovules, pistil, and petals