Compared to the flower and the fruit, the anatomy of the strawberry leaf and stems seems like it would be much simpler. But it’s not. To begin with, strawberry leaves are trifoliate, meaning that there are three leaflets for each leaf (Fig. 1). Leaves are connected to the crown by a stem called the petiole. The petiole branches connect each of the three leaflets via a petiolule. I doubt many readers knew the term “petiolule” until now. The leaflets have a serrated or saw-toothed leaf margin.

At the tip of each tooth/lobe of the serrated leaf margin is a specialized cell called the hydathode. This specialized pore is connected to the plant’s vascular system (or plumbing if you will) and serves to regulate fluid balance by releasing excess water in a process known as guttation (Fig. 2).

You’ll typically see guttation in the early morning hours as a drop of water from each hydathode. Remember that the sepals (the leaflike structures that form the calyx) are also a type of leaf, and thus have hydathodes and produce guttation in the same manner (Fig. 2). This drop of water is actually mineral-rich plant sap and not dew, which is why it often leaves a white residue. Depending on the type and concentration of minerals in the guttation, it can burn the margins of the leaf (Fig. 3).

Leaves are where photosynthesis occurs and anything that reduces the leaf’s surface area will reduce photosynthesis and thus plant health. This includes our most common diseases such as angular leaf spot, powdery mildew and Zythia leaf blotch (Fig. 4). It also includes abiotic leaf injury such as phytotoxicity from sprays or mechanical injury from wind and insect feeding (Fig. 5).

Another important feature of the leaf is the stomate (plural = stomata). These are openings in the leaf surface, exclusively on the underside, where gas exchange or respiration occurs. All above-ground plant parts have stomata, but they are much more numerous on the undersides of leaves. Stomata are bounded by guard cells that swell and shrink to close and open the pore, taking in carbon dioxide needed for photosynthesis and releasing oxygen as a byproduct. Through these same stomata, water vapor escapes in the process known as transpiration. This release of water vapor from leaves pulls water up from the soil through the roots. Stomata will open and close in response to light, temperature and humidity. Typically, stomata open during the day when sunlight and water are used in photosynthesis and close at night when there is no light for photosynthesis and to conserve water.

Stomata also occur on stems. When a stem connects the leaf to the crown, it’s called a petiole. When it connects fruit to the crown, it’s called a pedicel or a peduncle depending on if there is branching. A peduncle branches to form multiple petioles which connects to individual fruit. The entire inflorescence is called the truss (Fig. 6).

Another important feature of strawberry leaves are the trichomes. We commonly refer to trichomes as leaf hairs and they are found on all above-ground plant parts but are particularly numerous on petioles and lower leaf surfaces, especially the leaf veins. In general, trichomes function to reduce moisture loss and provide a physical barrier against pests and diseases.

In strawberries, two types of trichomes are present: glandular and non-glandular. Non-glandular trichomes are long, single-celled structures and are the ones most visible on the undersides of leaves and along stems (including petioles, pedicels, and peduncles). Glandular trichomes are smaller and multicellular, consisting of a base, stalk, and head (Fig. 7).

Both types serve as physical barriers against insects and pathogens, and glandular trichomes can also secrete chemicals that accumulate on their surface. Trichome density varies widely among cultivars, a topic that has been studied extensively—but I’ll save that discussion for another blog post.