Cannabaceae

Cannabaceae is a specialized family of flowering plants. Many people know them as the hemp family. This group includes about 170 different species. These species are organized into roughly 11 different genera. The most famous members include Cannabis, which we call hemp. Another important member is Humulus, which we call hops. The largest group in this family is the genus Celtis. This genus contains about 100 different species of plants.

Members of the Cannabaceae family grow in very different ways. Some species are tall trees, such as those in the Celtis genus. Others are erect herbs that grow straight up. Some are twining herbs that climb using their stems. The leaves often have a shape called palmately lobed. This means the leaf lobes spread out from a single point. These plants also always have stipules, which are small parts at the base of a leaf. Most members have cystoliths, which are tiny mineral deposits in their cells. Some may also have laticifers, which are tubes that carry a milky fluid.

These plants have a unique way of reproducing. Many species are dioecious, meaning there are separate male and female plants. The flowers are actinomorphic, which means they have radial symmetry. They do not have large or colorful petals. This is because they are pollinated by the wind rather than insects. Because of wind pollination, the calyx and corolla are very small. These parts are reduced to vestigial remnants that coat the seed. A tiny, cup-like structure called a bracteole protects the seed. This bracteole is often mistakenly called a calyx by some people. The flowers grow in groups called cymes. In dioecious plants, male flowers form long structures called panicles. Female flowers are shorter and have fewer blossoms. The fruit can be an achene or a fleshy drupe.

Scientists have changed how they classify these plants over time. Before the 1990s, experts used different systems to group them. Systems by researchers like Cronquist and Dahlgren placed them in the order Urticales. This order included other families like Moraceae and Ulmaceae. However, new molecular data changed this view in the 1990s. This data showed these families actually belonged in the order Rosales. In 1998, the Angiosperm Phylogeny Group placed them in this expanded order. They are now part of a group known as urticalean rosids.

The history of Cannabaceae goes back millions of years. They likely originated in East Asia during the Late Cretaceous period. Scientists found very old pollen in Sarawak, Borneo. This pollen dates back to the Turonian age, about 90 to 94 million years ago. In the early Cenozoic era, these plants lived across the Northern Hemisphere. As the climate changed during the later Cenozoic, their range shifted. They moved toward more tropical regions of the world.

Humans have interacted with these plants for a very long time. Carbon dating suggests plants in the Cannabis genus were used in Xinjiang, China. This use for ritual or medicinal purposes may date to 494 B.C. Today, Humulus lupulus, the common hop, is very important for making beer. The resins in the hop flowers provide a bitter taste. These resins also have antimicrobial qualities that help extend shelf life. Some people even eat the young shoots of hops as a vegetable.

We use many species in the Cannabaceae family for different purposes. Some Cannabis plants are grown as hemp to produce fiber or oil. Their seeds are nutritious, and their leaves are edible. Other plants are grown for medical or recreational uses. People use dried flowers, extracts, or infused foods. Through selective breeding, humans can change the plant's chemistry. They can increase or decrease levels of THC or other cannabinoids. They can also change the terpenes to create scents like strawberry or citrus. Finally, the bark of the Pteroceltis tree is used to make high-end Chinese paper.