Some words are unrelated, yet curiously sympathetic – road and rode, wrote and rote, die and dye… Carpel and Carpal fall in that category. They sound the same, and both words have to do with individual parts that may function together. But any relationship has only to do with their etymological roots. Carpel comes to us through the association with fruit (karpos Gr = fruit) while carpal evolved as a medical term that refers to the wrist (also karpos in Gr = wrist), which tells us the confusion and connection go back thousands of years. In contemporary English, spelling is defining. The blocky wrist bones so clearly shown in the early X-ray (1896) on display in The Huntington’s exhibit “Beautiful Science” are carpals.
Beyond the Greek “karp” that anchors hands and fingers, botanists have adopted the fruit-related Greek “karp” in the form of carpel, as the term for each segment in a pistil. In ‘Valencia’ oranges from the Huntington citrus groves, you see segments (i.e. carpels) in cross-section.
But looking at Oranges gets us ahead of the story. To botanists, a pistil (therefore, a fruit) is made of one or more leaves. Many flowers, such as legumes, have a simple pistil made of a single carpel – which botanists consider a fertile leaf. Opening a Sugar Snap Pea gives clear evidence as to that relationship, in which the single carpel almost looks like a leaf
Peas have one pistil made of a single carpel. Other kinds of plants, like Magnolia and Peony, have more than one pistil in a single flower, each pistil remaining a separate structure, a separate carpel.
So carpels can be confusing. Thanksfully, peas are straightforward: one flower makes one pistil which consists of one carpel. And the Magnolia is reasonably intelligible: one flower makes many pistils, each pistil made of one carpel. In citrus, we have to get used to the very normal fact that one flower has one pistil, which can be made of many segments, i.e. many carpels. Botanists get a lot of mileage out of knowing how many segments are in each fruit, because internal fruit structure tends to be something that remains standard for plant groups. Since it’s usually easy to determine the number of segments, that characteristic can help significantly when we are trying to identify a plant.
This brings another useful pair of botanical words into play in the discussion – connate and adnate. When several carpels grow beautifully together in a pistil, making a single fruit that is segmented internally, we say the carpels are connate – which means that similar organs have melded, i.e. grown together as one. Connate shows up in morphological discussions, as does its alter ego, adnate. Adnate means that two different kinds of organs have grown together seamlessly, like a leaf growing attached solidly to a stem, or a stamen attached to a petal.
In lemons and oranges, the many carpels normally form a single fruit that is seamless from the outside. But things can happen. Growth of a developing pistil can be impacted, such that the carpels fail to become fully connate, which means you may find lemons that show incomplete union.
In Buddha’s Hand lemon, the failure is genetically-based. Carpels never grow fully connate.
This isn’t the end of terminology and confusion in the world of Carpology (yes, it is a word). There’s a full range of possibilities. And there are more etymological quandaries. At some future point, we’ll look into the relationships between pistil and pistol. In the meantime, check out some other examples below.