From a 4-centimetre wild gourd to a pumpkin heavier than a tonne
Wild squash fruits can be as small as 4 centimetres across. In 2014, Beni Meier of Switzerland set the world record with a pumpkin weighing 1,054 kg. Both belong to Cucurbita, a genus from the Andes and Mesoamerica whose shapes vary so wildly that single species were once mistaken for several.
Five species were domesticated: argyrosperma, ficifolia, maxima, moschata and pepo. Depending on variety and local habit they get called squash, pumpkin or gourd. All five can serve as winter squash because ripe fruits keep for months, though some pepo types, like zucchini, are best eaten young as summer squash. Butternut belongs to moschata, while maxima traces back to Argentina, Bolivia and Ecuador. The figleaf gourd, ficifolia, breaks the pattern by looking nearly identical from plant to plant. Botanists count anywhere from 13 to 30 species in total, all carrying 20 pairs of chromosomes.
Each plant carries separate male and female flowers, yellow to orange, growing singly from the leaf joints. Most gourd-family males have five stamens; Cucurbita males have three, fused so tightly they look like one. In North and Central America, specialist squash bees of the genera Peponapis and Xenoglossa can make the difference between a flower that sets fruit and one that withers. The amount of pollen matters too: a heavily dusted stigma yields more seeds, bigger fruit and even faster-germinating offspring, an effect called xenia. Competitive growers hand-pollinate for exactly that reason.
Hormones steer the whole process. Ethylene pushes a plant toward female flowers, while gibberellin made in the stamens is needed to build the males. Once one fruit starts swelling, later female flowers tend to fail and males multiply, a pattern known as first-fruit dominance tied to falling ethylene in the stem. Farmers can counter it with ethephon, a product the plant turns into ethylene. Self-pollination still produces fruit, but inbreeding shrinks seed counts and size.
Not every species is a garden vine. A second group lives in dry country as perennials with storage roots, including the buffalo gourd, foetidissima, known by names such as stinking gourd and coyote gourd. It crosses with all the common cultivated squashes, so breeders use it as a bridge between species that otherwise stay apart.
Source: Cucurbita
