A Seminole pumpkin in a CSA box a decade ago got me thinking about squash diversity. Market bins and seasonal displays that autumn overflowed with squashes, gourds, and pumpkins in a dizzying array of sizes, shapes, and colors, but I had never seen a Seminole pumpkin among them. My pumpkin was squat, round, and the size of a cantaloupe. Its smooth, matte tan skin exactly matched the exterior of a butternut squash. The dense, dark orange flesh in its interior matched, too. It turns out that there is a good reason for this similarity: butternut squashes and Seminole pumpkins are different varieties of the same species, Cucurbita moschata. The pureed squash inside a can of commercially canned pumpkin is yet another variety of C. moschata, the Dickinson pumpkin, developed in the early 1800s by a Kentucky farmer named Elijah Dickinson. C. moschata boasts numerous other varieties, names of which variously include “squash” or “pumpkin”, but it is rarely the most well represented squash species at the market. That honor usually goes to Cucurbita pepo, followed closely by Cucurbita maxima, two of the five species of Cucurbita whose fruits appear on our tables as tender-skinned summer squashes or hard-shelled winter squashes.
Squash origins
All Cucurbita species are native to the Americas, a dozen or so species with scattered wild distributions, mostly in Mexico. Cucurbita fruits were important dietary staples for indigenous peoples from Central America to New England. Domestication of at least five Cucurbita species predated European exploration of the Americas by several thousand years. C. pepo may have been domesticated in Mexico by ten thousand years ago, around the same time that wheat was domesticated in the Mediterranean. The word “squash” is derived from askutasquash, meaning “that which is eaten raw or uncooked” in the Algonquian language Narragansett, spoken by some indigenous groups of northeastern North America.
It may seem surprising to think of winter squash as raw or uncooked, but drying strips of the raw fruit was a common means of traditional preparation and preservation throughout the Americas. The Massachusett and Wampanoag peoples of New England had an additional word, pôhpukun, to describe the squashes they grew that “grow forth round.” This word was transmogrified into “pumpkin” by the 17th-century English colonists made famous by tales of the first Thanksgiving. The indigenous word was conveniently similar to the Early Modern English word for Eurasian melon, pompion, which was familiar to Europeans of the period.
C. moschata proved particularly hardy in the swampy lands of what is now the southeastern United States, traditionally home to numerous tribes, including the Seminole. The squash that now bears their name grows as a sprawling plant with the huge palmate leaves and curling tendrils typical of cucurbits, members of the gourd family (Cucurbitaceae), which also includes cucumbers, melons, and gourds (and loofah!). Accounts of early Spanish explorers to Florida describe Cucurbita vines twining up tree trunks, with their pendulous fruits hanging over rivers or decorating the dead oaks that the Native Americans used as trellises to farm the squashes. The large nutritious seeds inside the fruit were as important a food source as the sweet flesh. Unsliced fruit could be stored for months, protected by the hard outer shell.
Squash hardiness is usurprising given the means by which cucurbit lineages initially arrived in the Americas. The family Cucurbitaceae arose near modern-day India in the late Cretaceous, around 63 million years ago. The leading hypothesis for how ancient cucurbits migrated from the Asian subcontinent to every other continent except Antarctica is transoceanic long-distance dispersal. That is, either the tough-shelled fruits floated across the ocean, or the seeds were carried in the guts of birds. Ancestral cucurbits made the journey from Asia to Africa, and then from Africa to South America. The jump from Africa to South America happened approximately five times over the course of several million years. The descendants of those five founders eventually radiated into around 350 modern cucurbit species in the Americas. The genus Cucurbita originated between 9 and 23 million years ago in Central or South America. Cucurbita expanded its range into North America by the onset of indigenous American agriculture, around 10,000 years ago.
Five species, many varieties
Those northern radiations of the genus resulted in the three highly variable species that constitute the vast majority of pumpkins and other squash consumed in the world: Cucurbita pepo, C. moschata, and C. maxima. Two additional Cucurbita species, C. argyrosperma (cushaw) and C. ficifolia (fig-leaf gourd), are cultivated in a few areas, mostly in Mexico and Central America. Most of the squashes that come to mind when you think of “pumpkin”—large Jack-O-Lantern pumpkins, orange sugar pumpkins, squat mini pumpkins, white Casper pumpkins—are varieties of Cucurbita pepo. C. pepo also includes acorn squash, delicata, stringy spaghetti squash, and most of the summer squashes—zucchini, yellow crookneck, pattypans, and marrows. C. maxima includes the Hubbard, turban, and kabocha squashes. Distinct named cultivars of these Cucurbita squash species have been developed through selective breeding over centuries, and most are totally interfertile within a species, and the species do occasionally hybridize.
Summer squash cultivars–especially the zucchini, yellow crookneck, and vegetable marrow cultivars of C. pepo–have been developed for their tender, immature fruit. These fruits are meant to be picked well before seed maturation. If left on the plant to mature, summer squashes will develop the hard rind and woody seeds that characterize their winter squash brethren. European explorers introduced hard-shelled American Cucurbita to the rest of the world starting in the early 16th century, and the agricultural development of summer squashes occurred primarily in Europe subsequently. Most squash varieties, however, have been developed under selection for various characteristics of the mature fruit. At least one variety in Mexico was developed primarily for the mature seeds—pepitas—a staple of Oaxacan cuisine. Much is known of the genetic basis of the tremendous morphological variation among Cucurbita species. We largely understand the genetic architecture of fruit shape, shell lignification (becoming hard and woody), color, size, and beta carotene content (carotenes—Vitamin A precursors—make the fruit of most winter squashes yellow to orange). A white pumpkin, for example, expresses dominant alleles (gene variants) of two genes: Wf for white flesh and W for weak fruit color. A warty pumpkin has a dominant allele of the gene Wt. The traditional orange pumpkin has the right alleles for many genes responsible for the synthesis of orange carotenoid pigments, especially lutein and beta-carotene, and the “orange” gene Or encodes an enzyme that directs the differentiation of specialized plastids in fruit cells called chromoplasts in which those carotenoids accumulate.
A particularly interesting gene unique to C. pepo called sp controls the stringiness of the fruit. When a hapless C. pepo inherits two copies of the recessive allele (gene variant) of the sp gene from its parents, the fruit flesh will have “spaghetti” texture, breaking into long strands when cooked. Hence, the name for “spaghetti squash” or “vegetable spaghetti.” Anatomically the strings are separated by bands of pectin that disintegrate during cooking. As cultivars of C. pepo, Jack-O-Lantern pumpkins, acorn squash, and over-ripe zucchini can also be stringy. If you cook up your Jack-O-Lantern pumpkins after Halloween, you might have to put the flesh through the blender to puree the strings. The flesh of C. maxima and C. moschata tends to be firmer than that of C. pepo, and it cooks up smoother. This is undoubtedly why C. moschata is preferred as the “pumpkin” of choice for commercial canned pumpkin producers, and why I prefer C. moschata or C. maxima varieties for any recipe that calls for pureed squash, be it ravioli or pumpkin pie.
Turning pumpkin carving into a botany lab
Winter squashes are gloriously large fruits and are therefore excellent subjects for botanical observation. Carving a Jack-O-Lantern or cutting up a squash for a recipe becomes an instructive dissection when you know what to look for.
Botanists have names for different types of fruits. A squash is a pepo, a hard-rinded berry that develops from a flower with a single inferior ovary. “Inferior” means that the squash flower ovary is located within the hypanthium, the tissue that supports the petals and sepals. Squash plants make separate male and female flowers. Upon opening, the golden petals of female flowers are already subtended by a tiny squash—the inferior ovary and its protective tissue. The round brown circle on what we perceive to be the bottom of the pumpkin is the scar left after the petals and sepals fell off the developing fruit. As the fruit develops, the hypanthium tissue fuses with the outer wall of the ovary to become the exocarp rind, encasing the firm flesh of the mesocarp and soft endocarp. When you scoop out the stringy, gooey stuff and seeds from inside the pumpkin, you’re scraping out both the endocarp and the placental tissue that that connects the seeds to the ovary wall. The cavity of your pumpkin might look like it has lobes to it, called locules. I start the pumpkin carving by cutting out the lid around the “handle,” which is really the peduncle, the specialized stem that connects first the flower and then the developing fruit to the main plant stem.
Save the seeds! It’s a bit of a pain to separate the gooey fruit from the seeds, but salted and roasted pumpkin seeds is a real treat. Crack the hard seed coat (testa or integument) to reveal the olive-green-colored cotyledons (leaves) of the embryo, which take up most of the seed. The part of the embryo that will sprout roots is in the pointy end of the teardrop-shaped seed.
Seeds of ancestral Cucurbita species are present in fossilized mastodon dung deposits, which suggests that fruits of the genus were already adapted to dispersal by large mammals even before humans got involved with its evolution through domestication. There is evidence that some ancient Cucurbita speciesdeclined in geographic extent and abundance following the extinction of the animals that had pushed the evolution of its fruits toward large size and high sugar content. Humans arriving in the Americas essentially replaced the extinct megafauna and fundamentally changed the trajectory of the languishing Cucurbita, which in turn eventually became a crucial food source for the indigenous peoples of two continents.
I find this long view of the history of these plants and people to be a hopeful tale. It is as good an accompaniment to a Thanksgiving pumpkin pie—far more truly American than apple pie–as the whipped cream.
