Plant Anatomy

To understand what a plant needs, it is critical to understand what a plant is. Understanding of plant anatomy assists gardeners and park managers to identify what is affecting a plant’s growth and health while suggesting natural solutions to support the plant.

Plants can be sorted into two groups: Monocots and Dicots. a chiefly herbaceous angiospermous (flowering with seeds in fruit) plant (such as a grass, lily, or palm) having an embryo with a single cotyledon, usually parallel-veined leaves, and floral organs arranged in multiples of three. Dicots are an angiospermous plant (such as a deciduous tree or broad-leaved herb) having an embryo with two cotyledons, leaves with typically reticulate venation, and floral organs usually arranged in multiples of four or five.

In the image above, not the seed single lobe seed on the left vs the double lobed seed on the right. Also note the root structure. The monocot on the left has fibrous roots forming a mat while the dicot on the right has a main tap root and side shoots extending away from the tap root.

Monocots tend to have fibrous roots while dicots tend to have a main tap root with shoots coming off of it. Monocots such as turf grass create a mat of roots through which water has a difficult time passing. Dicots have a tap root and side shoots which go deeper into the ground and break up the soil allowing water to pass more easily. When addressing water runoff issues around a home or public park, dicots, especially native dicots allow water absorption decreasing standing water that draws mosquitos, local flooding and, when native plants are used, are more sustainable in our extreme weather. Turf grass should be minimized in this situation.

Plant structure can be characterized by roots and shoots.

Root functions are anchorage for the plant, absorption of water and nutrients, storage and propagation. Primary roots are the first root from the seed. For dicots that is usually the tap root. From the tap root are lateral shoots as seen in the image above on the right. For monocots the roots tend to be a fibrous mat as seen in the image above on the left.

Many plant roots can regenerate from its roots. To remove those plants, the entire root must be removed or killed. Around the root will often be found a fungus: mycorrhizae. This fungus absorbs sugar from the root but provides an added surface area to absorb more nutrients into the root. Consider soils and soil ammendments with this fungus to add in plant growth. Note in the images below the difference between the roots with mycorrhiza fungus and those without.

Shoots are composed of stems, twigs, leaves, buds, flowers. Stems support the leaves to mazimize light absorption, create a conduit for water, minerals, and nutrients and act as a storage site. Stems may be herbaceous or woody and have different structures as noted in the illustration.

Note how the stem increases in complexity from a monocot on the right to a dicot in the center to a woody stem on the right. The increased complexity in the stems are related to the increased complexity of the needs of the plant. The key tissues to note are the xylem and the phloem. The vascular system is comprised of two main types of tissue: the xylem and the phloem. The xylem distributes water and dissolved minerals upward through the plant, from the roots to the leaves. The phloem carries food downward from the leaves to the roots. Notice in the diagram that as the plant becomes more complex, the xylem and phloem increase in size. Which part of a plant is damaged or diseased can give clues to what tissues need to be treated and how to treat them. On a very practical note, consider collecting the sap of a maple tree for maple syrup. To collect the sap, the tap needs to be placed in the xylem in early spring so that the sap moving from winter storage in the root to growth parts in the leaves in the spring can flow out into the tap to be collected for syrup. However, if you tap into the xylem in too many places or in a circle, the tree will be weakened or die because ti is not getting enough sap to grow. From a pruning of the tree standpoint, the cut must remove all of the tissue of the limb being pruned without cutting into the tissue supporting the tree. Improper pruning can allow disease to enter the xylem and phloem or prevent the undifferentiated tissue from growing over and healing the cut. More on that in the section on Trees.

In the image above, to prune the right side, cut just outside (to the right) of the node from which the right twig grows.. That will remove the xylem and phloem to the right twig but still allow the undifferentiated tissue in the node to differentiate into a scar to cover over the cut preventing decay and disease of the main stem of the twig. Leaving more of the right twig allows the tissue outside the node to decay and diseases to enter the main twig before the scar can form.

Though they grow underground, modified stems are common. They include tubers (think potatoes), corms (think carrots) bulbs (onions), rhizomes (think irises or ginger) and runners (think strawberries).

Buds are simply undeveloped shoots. They contain leaves or flowers. The bud protects the tissues of the leaf or flower from cold due to their scales surrounding the leaf or flower tissue. Usually, buds require a chill to resume growing.

Leaves not only are necessary for food production for the plant, they create shade decreasing overall temperature in an area and oxygen as a byproduct of thier respiration. There are multiple leaf categories but the key ones are identified by their margins, variations, types and shapes. Using a dichotomous key (A dichotomous key is a method of identification whereby groups of organisms are divided into two categories repeatedly), leaves are key to identifying specific plants and trees.

So far, a dichotomous key of plants information that we have discussed would look like this:

A dichotomous key can be used to further identify types of leaves and ultimately types of trees. A dichotomous key for leaves would include yes no questions as to the category of the leaves, variations, types, shape, margins

To use the key to identify leaves, try this example. The yes/no questions on the right focus on category (as in the image above), arrangement of the leaflets, leaf shape, arrangement of the veins, overall shape and margins.

This process will be expanded when we discuss trees as the dichotomous key is helpful in identifying an unknown tree.

The flower and fruit. As above, the anatomy and terminology of the parts of the flower allow identification of the flower as well as a method to determine the health or disease state of a particular flower. As already discussed, the numbers of petals and sepals depend upon whether the flower is from a dicot (multiples of 4 or five sepals and petals) or monocot (multiples of three petals and sepals). Most flowers are monoecious (mono meaning one or all in one) meaning they have both male (stamens) and female parts (pistols) though a few are dioecious (di meaning two or needing two different plants to fertilize) meaning that some plants in the species are all male and others are all female. Examples of dioecious plants include holly, ginkgos, bayberries, junipers, pussy willows, ash trees, spinach and asperagus. When choosing plants for specific places this can be particularily important. For example female ginkgos are incredibly messy and holly berries are poisenous. For example knowing the type of flower prevents mistakes such as planting male and female hollies at a daycare or near pets which could be disastrous.

A fruit is a mature, ripened ovary, along with the contents of the ovary. The type of fruit formed depends upon how the ovaries form the seeds as seen in the diagram below.

Simple fruits, such as apples, tomatoes (yes, they are a fruit not vegetable), peaches, pears and plums are easy to differentiate from appregate fruits such as respberries and blackberries. Example of a multiple fruit is corn on the cob (yes, another fruit, not a vegetable). The seeds encased in the fruit will germinate under the right conditions to produce genetically variations of the parent species. Germination brings us back to the beginning of this section.