Year of Pollination: Hand Pollinating Cucurbits

Because of their large, open, unisexual flowers, plants in the gourd family are perfect for practicing hand pollination. There are several species in this family that are commonly grown in gardens, and all can be hand pollinated. Hand pollination of cucurbits is most often done when there are problems with pollination (lack of pollinators, etc.) or for seed saving purposes (i.e. to ensure that a variety breeds true). It can also be done just for fun, and that’s mostly what this post is about.

But first, if your goal is to save seeds and maintain the integrity of the varieties you are growing, there are a few things to keep in mind. Cucumbers, melons, and watermelons are all different species (Cucumis sativus, Cucumis melo, and Citrullus lanatus respectively), so you won’t have to worry about crosses between these crops. You will, however, have to worry about crosses between different varieties within individual species. So, for example, if you are growing multiple varieties of cucumbers – or if your close neighbors are also growing cucumbers – you should hand pollinate. Summer squash, winter squash, pumpkins, and some gourds are members of at least four species in the genus Cucurbita (C. pepo, C. maxima, C. mixta, and C. moschata). There is a possibility of hybridization between some of these species as well as between varieties within the same species, so precautions should definitely be taken when saving seeds for these crops. This can mean, along with hand pollination, placing bags over flowers so that bees are unable to bring in pollen from “the wrong” plants.

There are plenty of great resources about saving seeds that offer much more detail than I have gone into here, one of which is a book by Marc Rogers called Saving Seeds. Consult such resources if you would like to try your hand at seed saving. It’s easier than you might think, and it’s very rewarding.

Regardless why you are hand pollinating your cucurbits, the first step in the process is differentiating a male flower from a female flower. This is simple. Female flowers in the family Cucurbitaceae have inferior ovaries, meaning that the ovary sits below the area where the petals and other flower parts are attached. The ovaries are quite pronounced and resemble a miniature fruit. The male flowers lack ovaries, so instead are simply attached to a slender stem. You can also observe the sex organs themselves – male flowers have stamens, female flowers have carpels. Male and female flowers may also be located on different areas of the plant and may open at different times of the day. All that being said, the most obvious indication is the “mini-fruit” at the base of the flower or lack thereof.

Cucurbit flowers: male (top) and female (bottom) - photo credit: wikimedia commons

Cucurbit flowers: male (top two photos) and female (bottom two photos) – image credit: wikimedia commons

Once you have identified your flowers, you have a limited amount of time to hand pollinate them. It’s best to find flowers that are just starting to open, as the female flowers may only be receptive for as little as 24 hours. You can use a cotton swab to gather pollen from the male flower, or you can simply pluck the flower from the plant, remove the petals, and touch the pollen-loaded anthers to the stigmas of a female flower. Either way, you must get the pollen from the male parts of a flower to the female parts of a flower as that is the essence of pollination. Simply put, it’s plant sex. Play some soft jazz while you do it if you want to.

A honeybee in a squash flower

A female squash flower with honeybee inside

A honeybee covered in pollen drinking the nectar of a female squash flower

Honeybee covered in pollen drinking the nectar of a female squash flower

As with saving seeds, there are a lot of resources out there explaining the details of hand pollinating cucurbit flowers, including this guide from Missouri Botanical Garden and the following You Tube Video.

 

While we are on the subject of cucurbit flowers, it should be noted that squash flowers are edible and can be prepared in a variety of ways, as described in this post at The Kitchn. Just another reason to be impressed by this amazing group of plants.

The Gourd Family

Pumpkins are practically synonymous with fall. Outside of every supermarket, bins overflow with pumpkins and other winter squash; inside, shelves are stocked with pumpkin flavored, pumpkin spiced, and pumpkin shaped everything. It’s the season of the almighty gourd – a family of plants that not only shares a long history with humans but also features some of the most diverse and unique-looking fruits on the planet. They are a symbol of the harvest season, a staple of the Halloween holiday, and a family of plants that is certainly worth celebrating.

Chinese lardplant (Hodgsonia heteroclita) - photo credit: wikimedia commons

Chinese lardplant (Hodgsonia heteroclita) – photo credit: wikimedia commons

The gourd family – Cucurbitaceae – includes at least 125 genera and around 975 species. It is a plant family confined mainly to tropical/subtropical regions, with a few species occurring in mild temperate areas. Most species are vining annuals. A few are shrubs or woody lianas. One species, Dendrosicyos socotranus, is a small tree commonly known as cucumber tree. Plants in this family have leaves that are alternately arranged and often palmately lobed. Climbing species are equipped with tendrils. Flowers are unisexual and are typically yellow, orange, or white and funnel shaped. They are generally composed of 5 petals that are fused together. Male flowers have 5 (sometimes 3) stamens; female flowers have 3 (sometimes 4) fused carpels. Depending on the species, male and female flowers can be found on the same plant (monoecious) or on different plants (dioecious). Pollination is most often carried out by bees or beetles.

The flowers of balsam apple (Momordica balsamina) - photo credit: eol.org

Balsam apple (Momordica balsamina) – photo credit: eol.org

Vining habits and diverse shapes and sizes of leaves and flowers make plants in this family interesting; however, it is the fruits born by this group of plants that truly make it stand out. Known botanically as pepos – berries with hard or thick rinds –  their variability is impressive. Imagine just about any color, shape, size, or texture, and there is probably a cucurbit fruit that fits that description. Even the flesh of these fruits can be incredibly diverse. Some fruits are small and perfectly round; others are long, twisting, and snake-like or have curving neck-like structures. Some are striped, variegated, or mottled; others are warty, ribbed, or spiky. What’s more, the cultivated pumpkin holds the record for the biggest fruit in the world.

The spiky fruits of wild cucumber (Echinocystus lobata) - photo credit: wikimedia commons

The spiky fruits of wild cucumber (Echinocystus lobata) – photo credit: wikimedia commons

Having such unique fruits is probably what drew early humans to these plants. Bottle gourds (Lagenaria siceraria) were one of the first species of any plant family to be domesticated (more than 10,000 years ago). This occurred in several regions across the Old World and the New World even before agriculture was developed (more about that here). Today, numerous species in this family are cultivated either for their edible fruits and seeds or for seed oil and fiber production. Others are grown as ornamentals.

The genus Cucurbita is probably the most cultivated of any of the genera in the family Cucurbitaceae. Summer squash, winter squash, pumpkins  – all are members of various species in this genus. Cucumbers and melons are members of the genus Cucumis. Watermelon is Citrullus lanatus. Gourds are members of Cucurbita and Lagenaria. Luffa aegyptiaca and Luffa acutangula are grown as vegetable crops (the young fruit) and for making scrubbing sponges (the mature fruit). Chayote (Sechium edule) and bitter melon (Momordica charantia) are commonly cultivated in latin and asian countries respectively. And the list goes on…

Considering that there are so many edible species in this family, it is important to note that some are quite poisonous. The genus Bryonia is particularly toxic. Consumption can result in dizziness, vomiting, diarrhea, and ultimately, death. As Thomas Elpel states in his book Botany in a Day, “this plant is not for amateurs.”

White bryony (Bryonia dioica) - photo credit: wikimedia commons

white bryony (Bryonia dioica) – photo credit: wikimedia commons

Researching this family has been fun, and this post barely scratches the surface of this remarkable group of plants. One species in particular that stands out to me is Alsomitra macrocarpa, a liana from the tropical forests of Asia. Commonly known as Javan cucumber, this plant produces football-sized fruits packed with numerous seeds that are equipped with expansive, paper-thin “wings” that assist the seed in traveling many yards away from its parent plant in hopes of finding room to grow free from competition. Here is a video demonstrating this resourceful seed:

22 + Botanical Terms for Fruits

First off, let’s get one thing straight – tomatoes are fruits. Now that that is settled, guess what is also a fruit? This:

(photo credit: wikimedia commons)

(photo credit: wikimedia commons)

Yep. It’s a dandelion fluff. More accurately, it is a dandelion fruit with a pappus attached to it. Botanically speaking, a fruit is the seed-bearing, ripened ovary of a flowering plant. Other parts of the plant may be incorporated into the fruit, but the important distinction between fruits and other parts of a plant is that a seed or seeds are present. In fact, the purpose of fruits is to protect and distribute seeds. Which explains why tomatoes are fruits, right? (And, for that matter, the dandelion fluff as well.) So why the tired argument over whether or not a tomato is a fruit or a vegetable? This article may help explain that.

Before going into types of fruits, it may be important to understand some basic fruit anatomy. Pericarp is a term used to describe the tissues of a fruit surrounding the seed(s). It mainly refers to the wall of a ripened ovary, but it has also been used in reference to fruit tissues that are derived from other parts of the flower. Pericarps consist of three layers (although not all fruits have all layers): endocarp, mesocarp, and exocarp (also known as epicarp). The pericarps of true fruits consist of only ovarian tissue, while the pericarps of accessory fruits consist of other flower parts such as sepals, petals, receptacles, etc.

Fruits can be either fleshy or dry. Tomatoes are fleshy fruits, and dandelion fluffs are dry fruits. Dry fruits can be further broken down into dehiscent fruits and indehiscent fruits. Dehiscent fruits – like milkweeds and poppies – break open as they reach maturity, releasing the seeds. Indehiscent fruits – like sunflowers and maples – remain closed at maturity, and seeds remain contained until the outer tissues rot or are removed by some other agent.

Most fruits are simple fruits, fruits formed from a single ovary or fused ovaries. Compound fruits are formed in one of two ways. Separate carpels in a single flower can fuse to form a fruit, which is called an aggregate fruit; or all fruits in an inflorescence can fuse to form a single fruit, which is called a multiple fruit. A raspberry is an example of an aggregate fruit, and a pineapple is an example of a multiple fruit.

Additional terms used to describe fruit types:

Berry – A familiar term, berries are fleshy fruits with soft pericarp layers. Grapes, tomatoes, blueberries, and cranberries are examples of berries.

Pome – Pomes are similar to berries but have a leathery endocarp. Apples, pears, and quinces are examples of pomes. When you are eating an apple and you reach the “core,” you have reached the endocarp. Most – if not all – pomes are accessory fruits because they consist of parts of flowers in addition to the ovarian wall, such as – in the case of apples and pears – the receptacle.

Drupe – Drupes are also similar to berries but have hardened endocarps. Peaches, plums, cherries, and apricots are examples of drupes. A “pit” consists of a hardened endocarp and its enclosed seed.

Pepo – Pepos are also berry-like but have tough exocarps referred to as rinds. Pumpkins, melons, and cucumbers are examples of pepos.

Pumpkins are pepos.

Pumpkins are pepos.

Hesperidium – Another berry-like fruit but with a leathery exocarp. Oranges, lemons, and tangerines are examples of this type of fruit.

Caryopsis – An indehiscent fruit in which the seed coat fuses with the fruit wall and becomes nearly indistinguishable. Corn, oats, and wheat are examples of this type of fruit.

Achene – An indehiscent fruit in which the seed and the fruit wall do not fuse and remain distinguishable. Sunflowers and dandelions are examples of achenes.

Samara – An achene with wings attached. Maples, elms, and ashes all produce samaras. Remember as a kid finding maple fruits on the ground, throwing them into the air, and calling them “helicopters.” Those were samaras.

The fruits of red maple, Acer rubrum (photo credit: eol.org)

The fruits of red maple, Acer rubrum (photo credit: eol.org)

Nut – An indehiscent fruit in which the pericarp becomes hard at maturity. Hazelnuts, chestnuts, and acorns are examples of nuts.

Follicle – Dehiscent fruits that break apart on a single side. Milkweeds, peonies, and columbines are examples of follicles.

Legume – Dehiscent fruits that break apart on multiple sides. Beans and peas are examples of legumes.

Capsule – This term describes a number of dehiscent fruits. It differs from follicle and legume in that it is derived from multiple carpels. Capsules open in several ways, including along lines of fusion, between lines of fusion, into top and bottom halves, etc. The fruits of iris, poppy, and primrose are examples of capsules.

Poppy flower and fruit. Poppy fruits are called capsules.

Poppy flower and fruit. Poppy fruits are called capsules.

Flowers and fruits are key to identifying plants. Learning to recognize these structures will help you immensely when you want to know what you are looking at. And now that it is harvest season, you can impress your friends by calling fruits by their proper names. Pepo pie, anyone?