Stems

Stems - they hold flowers up, leaves on, and don’t seem particularly interesting, but they are!

The word stem can refer to the trunk of a tree (aborescent), a bramble cane, a stalk, or a bine. [Bines are the stems of climbing plants, such as hops, that wrap themselves around external supports without the use of tendrils.]

Stem basics

Stems are the main aboveground stalk of a plant or shrub. [The roots are the below ground portion.] Stems can also be a limb that holds fruit, flowers, or leaves onto a larger limb. Stems perform four functions:

• stems provide structural support and they support leaves, flowers, and fruit
• stems hold the vascular bundle that carries water and nutrients between the roots and shoots
• stems store nutrients
• stems produce new plant tissue (meristems)

Stem showing internode and nodes plus leaf petioles (Knulclunk) Public Domain

Stem structure

On the outside, stems are usually divided into nodes and internodes. Nodes are areas that hold leaves. Nodes are also where buds, petioles, and even roots can emerge. Internodes refer to the distance between nodes. These two pieces of information can often help in plant identification.

​On the inside, stems have three basic tissues: the outer skin, or dermal layer, ground tissue, and vascular tissue. You may already know that vascular tissue consists of the xylem and the phloem. Ground tissue, or parenchyma, is the “everything else” of plant soft tissue. There is no ground tissue in woody stems. Stems of annuals are usually herbaceous, which means green and flexible. Since they lack a cambium layer, they do not tend to get very big around. Woody perennials have a tough outer layer that gets wider each year.

Flax stem: Ep = epidermis; C = cortex; BF = bast fibers; P = phloem; X = xylem; Pi = pith (Curtis Clark)

Dicots, eudicots, monocots, and gymnosperms 

Most plants used to be classified as monocots (grasses), dicots (beans), or gymnosperms (pine trees). Recent genetic research has taught us that dicots are better described as a new new group, called eudicots. These different plant classifications have unique stem structures, when seen in cross section. Eudicot stems contain pith. Pith is the spongy material you see inside a sunflower stem. They also contain bast fibers. Bast fibers are what we harvest to make linen from the flax plant, and they protect the phloem. Vascular bundles form a ring near the outer edge of the stem. Monocot stems have vascular bundles scattered throughout the stem. Gymnosperms are similar to eudicots, except they use tracheids as part of their vascular system.

​Stem variety

Most stems are pretty obvious, and some, like the sunflower, can be substantial. That is, of course, until you consider that a redwood tree trunk is also a stem; A monumental stem, weighing in at 50,000 pounds! The stems that hold up flowers are called peduncles. In flower clusters, or inflorescences, the stems are pedicels. Sometimes, plants have stems so short that it looks like the leaves grow right out of the ground - these are called acaulescent stems.

Buds on twigs are also stems. Bulbs and corms are underground stems and leaves, but bulbs are more leaf than stem. Rhizomes are underground stems of many grasses, iris, and most ferns. [Most ferns don’t actually have an upright stem; instead, they have semi-rigid rhizomes.] Strawberry ‘runners’ are stolons, which are also stems. Potato plants also have stolons. Some stems grow in a tangled mess, or in low growing mats. This is called caespitose. Hostas, garlic, lilies, and iris have stems called scapes. Cacti and succulents have specialized leaves for holding a lot of water. Many of the “leaves” you see on these plants are actually flattened stems, called cladodes, that can perform photosynthesis.

Stems in the garden

Those melon and squash plants, the ones that send stems out along the ground, are called decumbent. You can remember that would because “dey come, bent up at de end.” [Hey, if it helps, why not?] Your shrubs have stems that are called fruticose.

Flower stems

As you have probably noticed, some flowers and fruit, such as sunflowers and raspberries, respectively, are actually made up of dozens, or hundreds of tiny florets. The single stem that holds up a sunflower head is called a peduncle, while each of the tiny stems that hold clusters of minuscule blooms are called pedicels. The thorns on your rose bush and the prickles on your blackberries are actually modified stems. So are tendrils. [Technically, rose thorns are not thorns at all. They are prickles, but I don't think we're going to change anyone's mind about that today.]

Food from stems

We get a large portion of our food from stems. Some may be familiar, but others may surprise you:

• asparagus
• bamboo shoots
• chicle, used to make chewing gum
• cinnamon, from tree bark
• gum arabic, a food additive
• kohlrabi
• maple sugar from maple tree sap
• nopalitos (cactus pads)
• sugar, from sugar cane
• water chestnuts

We also get things like camphor, quinine, and lumber (and all it’s related products) from the stems of plants. Many people assume that celery is a stem, but it isn’t. Celery is the stem that supports a leaf, making it a petiole, or leaf stalk. The stem of a celery plant is actually the round stubby base.

Stem pests and diseases

Stems are usually pretty well protected, but that isn’t always enough. Young stems infected with damping off disease are usually doomed from the start. Crown gall can cause lesions on stems. Other diseases that can appear on stems include peach leaf curl, blackleg, mummy berry, stem blight, anthracnose, Phytophthora tentaculata, black spot, and bacterial speck. Bagrada bugs, cutworms, eriophyid mites, katydids, crickets and grasshoppers, weevils, and harlequin bugs will feed on stems. Also, many pests use stems as hideouts and egg laying territory, so keep your eyes open!