Botany Terms Starting With I

Imbricate describes an arrangement of petals, sepals, bracts, or leaves in which each part overlaps the edges of its neighbors, much as roof shingles overlap one another.

In floral buds, imbricate aestivation means that each petal or sepal has one margin covered by the adjacent part and the other margin covering the part on its opposite side, producing a consistent, layered pattern around the bud. This arrangement is one of the primary aestivation types used in plant taxonomy to distinguish families and genera, alongside valvate aestivation, where parts meet edge to edge without overlapping, and contorted aestivation, where all parts overlap in the same rotational direction. Camellia (Camellia japonica) displays imbricate sepal arrangement clearly, with each sepal progressively larger toward the outside of the bud.

Beyond flowers, imbricate patterns appear in the overlapping bud scales of horse chestnut (Aesculus hippocastanum) and in the bracts of many pine cones, where the overlapping geometry reduces water loss and physical damage to enclosed tissues.

Inflorescence is the arrangement of multiple flowers on a single specialized stem axis, including forms such as the dense head of a sunflower, the elongated spike of wheat, and the branching panicle of oats.

Botanists classify inflorescences into two broad categories based on how flowers open: racemose types, in which the oldest flowers are at the base and the youngest at the tip, and cymose types, in which the terminal flower opens first. Racemose forms include racemes, panicles, spikes, corymbs, and umbels, while cymose forms include monochasial and dichasial cymes. Grouping many flowers together on one axis increases the visual target for pollinators and can improve pollen transfer efficiency compared with solitary flowers.

Inflorescence architecture is among the most diagnostic characters in plant taxonomy, helping botanists distinguish families such as Asteraceae, with its composite heads, from Apiaceae, with its compound umbels.

Internode is the section of a plant stem located between two consecutive nodes, forming the elongated cylindrical segments visible between leaf attachment points.

Internode elongation is driven by cell division and expansion in the subapical zone just below the shoot apex, regulated by gibberellins, auxin, and brassinosteroids. Light quality strongly influences this process: stems growing in shade produce longer internodes as the plant extends toward brighter light, a response called shade avoidance. Short internodes produce compact, bushy plants, while long internodes produce tall, open shoots, making internode length a key trait in crop breeding.

In maize (Zea mays), breeders have selected for specific internode lengths to optimize lodging resistance and harvest efficiency, with modern varieties typically producing 8 to 20 internodes per plant depending on the cultivar.

Iridoids are a class of monoterpenoid secondary metabolites found in many flowering plants, characterized by a cyclopentane ring fused to a six-membered oxygen-containing ring and typically occurring as bitter-tasting glycosides that deter herbivores.

Iridoids occur widely across plant families including Plantaginaceae, Lamiaceae, and Verbenaceae, where they accumulate in leaves, stems, and fruits as glycoside conjugates. Their bitter or acrid taste deters generalist herbivores, and when hydrolyzed by digestive enzymes, the released aglycone forms can disrupt digestion or produce neurological effects in vertebrate and invertebrate consumers. Some specialist insects in the order Lepidoptera and certain beetle families have evolved tolerance to iridoids and sequester them from host plants for their own chemical defense against predators.

Aucubin and catalpol are among the best-studied iridoid glycosides, found at concentrations of up to 10 percent dry weight in some plantain (Plantago) species.