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Home / Blogs / Knowledge is Power; Know Your Flowers (Part 1) – An Inflorescence Story
March 11, 2024
Spring is upon us. The days are getting longer and the weather is getting warmer; this seasonal shift begins the emergence of blooms. Flowering plants, while so charismatic, are a complex set of organisms. If you’ve ever spent time looking closely at different flowers (which I highly recommend) you’ve likely noticed how vastly different and complicated these structures can be. An important step in appreciating these differences is to know how botanists are categorizing the diverse types of patterns they notice in flowers. Are you searching for an article to expand your botanical vocabulary before the spring blooms, so that you can fully enjoy the flowers you find? Look no further…
First, let’s talk about the plant kingdom; did you know that not all plants produce flowers? Kingdom is the broadest hierarchy in biological classification; remember the mnemonic King Phillip Came Over For Good Soup? The plant kingdom can roughly be divided into four main Phyla. The “least” evolved, Bryophytes, are our non-vascular plants, meaning they do not have specialized tissues for transporting water or nutrients. Mosses, liverworts, and hornworts make up Bryophytes. A step up evolutionarily, is the phylum that contains Pteridophytes and Lycophytes (think ferns and other spore bearers). These are our vascular plants (these plants contain those specialized tissues for water and nutrient transport mentioned above) that do not bear seeds. Next comes Gymnosperms, they are our “naked” seeds, generally meaning the seeds are exposed on cones. Gymnosperms encompass conifers, cycads, and a few other plant varieties. Our “most” evolved plants are angiosperms. These are our flowering plants that will be discussed more in-depth.
An important distinction in angiosperms is between monocotyledons and dicotyledons. Monocotyledons or monocots are those that produce one cotyledon, the first leaves to appear from a germinated seed. This is characteristic of grasses, however Liliaceae (Lilies), Alliaceae (Alliums), Orchidaceae (Orchids), and even Arecaceae (Palms) are monocots. Monocot flowers generally have parts in threes or pairs of threes. Take Lilium superbum (Turk’s cap lily) for example; the native flower has two whorls of three stamens and three styles (don’t worry if you don’t know these plant parts, we’ll discuss what these are in part 2 of Know Your Flowers). Dicotyledons, or dicots, have two cotyledons. Dicots encompass herbaceous flowering species, and generally have flower parts in fours and fives.
With this basic knowledge, let’s jump into flowers. A flowering plant can be monoecious (Greek for “one house”), meaning it is a species with male and female reproductive structures on the same individual. A flowering plant can also be diecious (Greek for “two houses”). This refers to the species having male and female structures on separate individuals. Plants, however, can produce varying combinations of flowers during their lifetime; this variance can be attributed to geography, climate, resource competition, life stage, and other factors.
Variance can also be found in plant inflorescences. Inflorescence refers to how groups of individual flowers are arranged on a stem. Botanical vocabulary that you’ll often hear surrounding inflorescences are peduncle and pedicle. The peduncle is the main stalk of the inflorescence, and the pedicle is the stalk of an individual flower within the inflorescence. Inflorescences are generally considered to be monopodial or sympodial. Monopodial, sometimes referred to as intermediate, concerns development where flowers first open at the bottom of the inflorescence and move up. The peduncle does not terminate in a flower, allowing for indeterminate growth. Sympodial, or determined, inflorescences have flowers that first open at the terminal end and then open as they descend the inflorescence. For sympodial inflorescences, the peduncle terminates in a flower and the number of individual flowers is predetermined. Below are some inflorescence types:
Solitary flowers are those that form apart from another flower. These flowers are usually large in size. A solitary flower you may see this spring is Aquilegia canadensis, or Eastern Red Columbine. The species has a branching flowering pattern, but notice each individual flower has a respective peduncle.
Raceme flowers arise from the main stem, similar to spikes, but each individual flower has a pedicle. Racemes are notoriously unbranched and indeterminate in growth. This summer when you discover cardinal flower, or Lobelia cardinalis, notice that each red flower has a pedicle.
A spike inflorescence is one in which the flowers arise from the main stem without individual pedicles, this means the flowers are sessile (they arise directly from the peduncle). Carex stricta, common name tussock sedge, has a spiked inflorescence in which male and female spikes are separate.
A panicle is similar to a raceme, but is branched. So each branch of the panicle maintains a smaller raceme, and the terminal bud does not produce a flower. A panicle to keep your eye out for this summer is Eutrochium fistulosum, Joe-Pye Weed.
Cymes are sympodial; the inflorescence will terminate in a flower. With cymes, the central flowers open first and the peripheral flowers proceed. Cymes will often have the appearance of being flat, like Allium cernuum or nodding onion.
A verticillaster inflorescence is whorled, meaning the flowers form in rings up the stem. Verticillaster growth is indeterminate. Stachys tenuifolia or smooth hedge nettle follows this flowering pattern.
Pedicles in an umbel are all the same length; this gives umbels a round appearance. Platanus occidentalis, our admired sycamore tree, has an umble type inflorescence.
Corymbs are characterized by pedicles varying in length to create a cluster of flowers that are all at the same level. Arrowwood viburnum or Viburnum dentatum, forms beautiful white corymbs in late spring.
A spadix is similar to a spike in that many flowers are arranged on the peduncle, but in a spadix the flowers are sheathed in a specialized bract (modified leaf tissue), called a spathe. Eastern skunk cabbage or Symplocarpus foetidus, is a spadix. The splotchy maroon to green leaf-like structure that first appears is the spathe. The spathe swaddles the spadix which appears almost cone-like.
A capitulum is characteristic of Asteraceae, the daisy family, in that disc and ray florets (more on these in part 2 of Know Your Flowers) are arranged atop a receptacle. Many Symphyotrichum and Helianthus species are examples of a capitulum.
Catkins are apetalous, they have no petals, and are unisexual in a spike-like arrangement. Salix sp. as well as Alnus sp., our willow and alder species, form catkin inflorescences.
Now that we’ve discussed the ways that groups of flowers can be arranged, let’s pause to get outside and enjoy a local skunk cabbage spadix. Next month we’ll dive into the characteristics of individual flowers, just in time for redbud and flowering dogwood blooms!
Photo credits from Plant Kingdom graphic:
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