Iris Flowers: Terminology and Structure

Irises are beautifully complicated flowers. In order to identify the species I’d found, I needed to understand how irises are described, and how they’re structured.

Irises are monocots. Monocots usually have different growth forms and habits from dicots. This group of leaves arising fan-like from a single point is a typical (though not universal) characteristic of monocot plants. Looking closely you’ll see parallel veins, also typical of monocots, although there are dicots with parallel venation.

Dicot flowers mostly (but not always) have parts in fours or fives, or multiples of. Monocot flowers are mostly in parts of threes, or multiples of.

Irises have three sepals and three petals. The sepals lie more or less horizontally, and have brightly colored central sections called signals.

(Click on each picture for a larger view.)


The abruptly narrowed part toward the inside is sometimes called the claw. The stamen is above it, hidden by the style arm.



A flower’s gynoecium (“female” part) is called the pistil; it consists of a stigma, which receives pollen, and a style, which connects the stigma to the ovary. In irises, the style is often called the style arm or style column. It’s the petal-like structure lying atop the sepals, covering the claws. The two curled lips on the ends of the style arms are the stigmas. The petals are more or less vertical.

The ovary is below the rest of the flower (this is termed inferior), and looks like a swollen part of the peduncle.




Surrounding the emerging buds is the leaf-like spathe.




Horticulturalists refer to the sepals as falls and the petals as standards, but I’ve never seen these terms used in botanical sources.

tomorrow: the differences between I. versicolor and I. virginica

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