Plant Morphology, Anatomy and Reproduction

Morphology is the study of the physical characteristics and structures of organisms.

This module will provide you with the basic botanical vocabulary to describe the primary features of a plant.

Once you begin to explore the taxonomy of the plant kingdom, one of the first ways to narrow down your search for a positive ID is to determine whether your specimen is vascular or non-vascular.

“Vascular” refers to the system of specialized tissues that conducts water and minerals through a plant. These are also sometimes referred to as the “higher” plants, to distinguish them from their “lesser” or more “primitive” peers.

Non-vascular plants are also known as bryophytes, and these are the mosses, liverworts and hornworts. We won’t go much deeper than that with these little guys, cute as they may be, ‘cause none of them are edible.

Our concern will be with the vascular plants, which are further categorized by their sexual organs.

The most valuable to us for food, by a landslide, are the angiosperms — flowering plants.

Other vascular plants include gymnosperms, which produce cones rather than flowers (think: pine tree), and ferns, which produce spores.

Growth Habit

“Habit” refers to the shape of the plant, and the traits up for consideration here include number of stems; stem length and shape; branching patterns; and more.

In general, you can usually narrow a species down to being a grass, a tree, an herb, a vine, or a shrub. There will always be cases that don’t fit neatly into any one category — tree-like shrubs, shrub-like vines, etc. — but growth habit can tell you a great deal about the plant’s ID and life cycle.

Also up worth considering here is the structure: is the plant herbaceous or woody?

Duration

“Duration” is the fancy scientific way of answering the question, “how long does it live?” Plants have several different potential durations, which shed light on their development, reproductive strategies, and their ecological roles.

Annual: the plant lives, reproduces and dies in a single growing season.

Biennial: the plant’s life cycle plays out across two growing seasons, often completing its herbaceous growth in the first year then reproducing and dying in the second.

Perennial: the plant lives more than two years, and often (but not always) takes several years to reach sexual maturity.

Monocarpic: the plant lives for several years, then dies after flowering and setting seed. (Contrasted with polycarps, those that flower multiple times across their life cycle.)

Structure

Your average, generic flowering plant will display the following general traits — don’t worry, we’ll go over all of these:

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All seed-producing plants are composed of two core components: roots and shoots.

Roots reach downward in search of water, key minerals and nutrients, and associations with mycorrhizal (fungal) networks in the soil; shoots reach upward in search of sunlight in order to produce leaves and reproductive organs.

For the majority of the plant’s life cycle, most of the real action is occurring at the tips of the roots and shoots: the apical buds, also known as meristems. This is where the plant is actively growing at any given time, producing new undifferentiated cells that will eventually become specialized tissues. It’s no coincidence that these are some of the most nutritious parts of edible plants — think: asparagus shoots.

As we make our way up from soil level, we encounter leaves growing at nodes along the stem, accompanied by axillary buds tucked in where leaf meets shoot.

Leaves are the organs with which plants photosynthesize and exchange water and gases with the atmosphere. They are composed of a blade — the main “body” of the leaf — and a petiole, which connects the leaf to the stem.

There are many, many scientific terms to describe the size and shape of leaves. It’s not very useful to just hand you a comprehensive list and ask you to memorize them, so instead we’ll learn them as we encounter them in the literature.

Leaves grow in relation to one another according to two patterns: they will either be paired — opposite one another along the stem — or else they will alternate, as with the example above.

(When it comes to trees and shrubs, branching patterns also conform to this opposite/alternate dichotomy. In fact, there are only a handful of tree genera with opposite branching patterns. If you can memorize them — there are acronyms for doing so — you’ll really step up your tree ID game. But that’s beyond the scope of this module!)

The axillary buds, located at the nodes, are embryonic shoots which often lay dormant for some period of time after developing, or until some signal is sent to the plant.

For example, if you want your basil plant to bush out, you need to pinch off the primary apical meristem up top in order to signal to the plant to awaken its axillary buds.

Tomato growers know runaway axillary buds as “suckers”, which are generally pruned off so that the plant will continue to devote its energy to its main stem rather than side shoots.

But axillary buds — since they’re embryonic, after all — can develop into vegetative shoots or reproductive shoots: flowers.

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Beginning at the base of the flower, we observe the bract(s), modified leaves which may or may not look different from other leaves on the plant.

Many flowers are connected to the stem via a stalk called a pedicel; those without pedicels are known as sessile flowers.

At the top of the pedicel we find sepals, sort of like halfway between a leaf and a petal in most cases, which serve to protect the flower when budding, and later support the petals when in bloom.

Petals are modified leaves that surround the reproductive organs. They are often very bright colors and sometimes feature ornate patterns that may or may not be visible to the human eye, but which serve to attract pollinators.

The morphology of a flower’s petals, along with its reproductive organs, offers many clues regarding the types of creatures that pollinate it.

Housed within the petals are the stamen and pistil, the angiosperm’s reproductive organs, which are roughly analogous to the sex organs of male and female animals, but far more complex in their own unique ways.

Some plants produce hermaphrodite flowers (both stamen and pistil present in each flower); others produce flowers of both sexes on one plant (each individual flower has only stamen or only pistil); still others will produce only male or only female flowers.

Some plants will happily self-pollinate; others require genetically dissimilar pollen from the same species to produce fertile seeds; still others will readily hybridize with related species in the area.

Further complicating all of the above, some plants may change sex or become hermaphroditic due to environmental signals such as heat stress, nutrient deficiency, drought, or cold.

Every one of these categories has its own special name, and some of them can be traced even further down into more specific subcategories. See how complicated this stuff can get? Good thing you’ve got a pal like me to break it down for you. ;)

Getting to know the sex parts a little better, in brief: the stamen is composed of a filament propping up an anther, where the pollen is produced. The stigma at the top of the pistil catches the pollen, which makes its way down the style and into the ovary.

Once pollinated, the ovary will swell up and mature into a fruit, the angiosperm’s mechanism of seed dispersal. The plant produces a big shiny sweet juicy fruit and persuades critters like us to eat it, and either we drop the seeds along the way or else they pass through our gut and are fertilized when they exit our systems on the other end.

To reiterate, this is really only scratching the surface of the morphological jargon used to describe plants, but if you can get a firm grasp on these foundational elements, you should be able to wade through the more technical stuff when we get to it!