The Anatomy Of Irises
How does one describe irises or the type of plants they are? To begin with, the foliage of irises is similar to that of grass, having similar parallel veining present in grasses, orchids and lilies. In addition, apparently the lance-like leaves of irises are without stems, but they normally grow right from the level of the ground. However, precisely speaking, the bulbs, rhizomes and corms of irises are actually modified stems.
The blooms of irises have a tripartite look. Typically, all iris flowers have three standards which are erect and three falls that are somewhat drooping. Together with their stunning hues, the standards and the falls add to the beauty and grace of the flowers making them enticing not only to the humans, but the pollinating insects as well. Once you take note of these botanical characteristics of irises, you will be able to understand them better.
All irises are flowering plants, scientifically known as angiosperms. According to a modest estimate, there are as many as 250,000 types of angiosperms or flowering plants on this planet. The leaves of irises have parallel veins and their flowering parts are always in multiples of three, which is a clear indication of the fact that they are monocotyledons. The term “monocotyledon” is used to describe plants having a solitary seed leaf, which is actually the third major evidence for monocots. The vascular bundles, or the circulatory structures of these plants, are yet another vital attribute of monocotyledons. Different from the ring system of the vascular bundles in dicotyledon plants, the circulatory arrangement of the monocotyledons is evenly distributed all over the plant tissue. For instance, lilies (botanical name Lilium spp.) as well as daylilies (botanical name Hemerocallis spp.) too are very familiar monocotyledon plants that are grown as ornamental plants in gardens across the globe.
As a group, monocotyledons are again divided into two groups – one that produces petaled flowers, such as the irises; and, the second, those that do not produce petaled flowers, such as members of the grass family (Gramineae).
These vascular bundles enclose tissues that are engaged in transporting water and nutriments right from the roots of the plants to their green foliage. These tissues are known as the xylem. A particular vascular tissue called phloem transports carbohydrates, which are produced by means of photosynthesis, from the foliage of the plants to their rhizomes, roots, and bulbs. As we are aware, only green plants possess the ability to manufacture nutrients required by the plants by making use of sunlight, water as well as carbon dioxide (CO2). As the green plants manufacture simple carbohydrates, they are always placed at the base of the food chain. In fact, all other life forms, including plants as well as animals, can track its continued existence to the green plants in the form of foods.
As discussed above, angiosperms (flowering plants) are classified into two groups – the monocotyledons and the dicotyledons. While monocots have a single seed leaf, dicotyledons have two seed leaves. The flowering parts of the monocotyledons are always found in three parts. On the contrary, the flowering parts of dicotyledon plans grow in multiples of four or five. Unlike the monocotyledons, the leaves of dicotyledons have netted veins and the arrangement of their vascular bundles is circulatory or in the form of rings. Roses, the flowering shrubs, zinnias, fruit trees and others in our garden are all dicotyledon plants.
Irises bear tripartite flowers that appear singly or in several numbers on the branched flower stalks. Each iris bloom has three standards, which grow upright, and three falls, which are somewhat droopy. While the standards can be described as the flowers’ petals, the falls form the sepals, which are either horizontal or turn downwards to the stem. Irises develop two modified leaves, which are often known as spathes. These spathes enclose one or additional flower buds. Their texture may be thick or thinner like a paper.
The spathes of different irises species differ in their color, size, shape, as well as texture. Hence, the spathes are often important in identifying the iris species. In addition, the spathes are also valuable while trying to assess the inheritance of the unidentified irises, as the attributes of the spathes may possibly be among the more noticeable distinctions that are passed on from the ancestral plants to the parent plants and eventually to the progenies.
Even the appearance, as well as the size of the iris blooms vary greatly, so do the relative size of their different parts. Apart from the fact that iris flowers come in an incredible assortment of hues, color combinations as well as color patterns, from one iris species to another all through the genus Iris, the flowers have an overall iris appearance, even as they display varied themes.
The main flower parts of irises comprise the three standards (petals), three falls (sepals), pistils (female reproductive organs including the style, stigma and ovary), stamens (male reproductive organs), and the perianth tube. In fact, the color as well as the color patterns of their standards and falls reflect the attributes or features of the different iris species and cultivars more distinctively. The perianth of iris flowers is made up of both the standards and the falls. The stamens of iris flowers bear their pollen, which are contained by the anthers at the top of the filaments (the stems of the stamens). In iris flowers, the stamens are positioned just below the style what is known as the “claw” of the iris branches.
The ovary of the iris flowers is considered to be “inferior”. In other words, this means that the ovary of iris is positioned at the base of the flowers. The perianth tubes of an iris flower encircle the pistils (female reproductive organ) and join the perianth with the ovaries. Precisely speaking, the ovary is the structure that bears the ovules and is found at the bottom of the flower. The ovules are fertilized when the tubes holding the pollen grains expand via the style to enter the ovary. The style is then connected to the ovary, which faces the falls. The branches of the styles have two small “wings”, which are known as crests, and they protect the stigma. The stigma is basically a rim or a lip positioned above the underside of the style branch. It is at this point that the pollen grains need to be deposited to start the pollination process.
Similar to the blooms of other plants, iris flowers have also evolved over several million years with a solitary intention – to grow seeds and, thereby make the plant’s future certain. The shape, color and usually the fragrance of the flower have a combined effect on drawing insects to it, thereby augmenting the prospects of pollinations as well as seed development. In the instance of irises, irrespective of whether it is the crest or bearded, the structure as well as the signal of the falls draw the insects and, at the same time, providing the pollinating agents with an appropriate space for landing on the flower.
When the pollinating insects move forward towards the flower tube containing nectar, they sweep the anther bearing pollens, thereby taking up the pollen grains on their body. As the insects move from one flower to another in search of more nectar, these pollinators also brush by the damp stigma of those flowers, depositing the pollen grains carried by them. The powerful microscopes available these days help the botanists to examine the pollen grains better. The apertures of these microscopes differ in various important ways and usually form the basis of classifying the irises.
Usually, the foliage of most irises is lance-shaped having a parallel veining system. However, a number of iris species show a lot of variety. Very often, the leaves of irises have a wax-like covering or bear flowers that have a greyish hue. Even the leaves’ textures vary from one iris species to another. Some iris species have thick leaves, while there are others whose leaf textures are relatively thin. The textures also vary from pliable to rigid and soft to hard. While the leaf fans are vertical, generally the blade of each leaf is wider at its base.
Iris leaves are inwardly folded along the edges serving as sheaths and helping to cleave to the leaves firmly together. Most plants belonging to the Iris genus usually produce flat, lance-like leaves. However, a number of iris species also bear leaves that are almost cylindrical shaped, square or channelled across. In the case of the leaves being channelled, their under surface is likely to have a prominent keel.
Depending on the underground structures of the irises, these plants can be grouped into two major categories. The plants in the first group have fibrous roots, in addition to modified stems known as rhizomes that generally grow in a horizontal manner and very close to the surface of the soil. All bearded irises belong to this group, which also includes other beardless species like the Pacific Coast, Siberian, Japanese, and Louisiana as well as spuria irises.
Plants in the second iris category also have fiber-like roots, in addition to bulbs, a different kind of modified stem that comprises plump scale leaves encircling a bud and a petite stem. The species that comprise this group include Xiphium (also known as the English, Dutch and Spanish irises), reticulated, and Juno or Scorpio irises. In fact, the Juno irises have a bulbous root and thick chunky roots for storing the plant’s nutrients. These attributes of Juno irises tell them apart from the Xiphium irises.
Interestingly, one iris species is between these two categories, as they neither have bulbous nor rhizomatous undergrowths. This particular iris species is Iris nepalensis. As the scientific name of this plant suggests, it is native to the temperate regions at the base of Himalayan Mountains, precisely speaking Nepal. In fact, the rhizomes as well as the bulbs of irises are basically meant for storing nutrients required by the plants and help the plants to sustain during the unfavourable climatic conditions.
The rhizomes as well as the bulbs of irises stock up moisture and nutrients, which are supplied to the plant when they require them, especially when the climatic conditions are extreme. The coating or external layer (also called tunics) of the bulbs vary, subject to the group to which the plant belongs. Some bulbs may have reticulated or netted coatings, while there are many others with leathery and paper-like or thick coatings. An iris plant may have very few or copious fibrous roots, subject to its type. Most tall bearded irises have thick fibrous roots, while the spuria irises usually have thin, sinewy fibrous roots.
A number of iris species, counting the evansia irises that are native to soggy woodlands, are able to spread via their stolons (thin stems that grow horizontally). These stolons emerge from the main plant close to the surface of the soil.
Irises that have rhizomatous undergrowths can again be divided into a number of categories, depending on their feature down the center of the falls of their flowers. For instance, all the pogon or bearded irises have a characteristic pattern of elongated hairs the length of the crest of their falls’ basal half and these hairs are known as beards. Some iris species bear crests, while there are other species that only have an even ridge. In many cases, iris flowers have signals on their falls, which are actually different color patches that distinguish those areas from the remaining part of the falls. These signals help to direct the pollinating insects, guiding them to the source of nectar following a path wherein the bodies of the insects will come in contact with the anthers as well as the stigmas of the flowers.
Similar to the iris flowers, their seedpods (also called capsules) also have three sections. However, these seedpods greatly vary in their shape and size. For the botanists, the flowers, seedpods as well as the seeds of irises are helpful in classifying the plants, particularly those having beards. While some iris seedpods are small, others have relatively long capsules. Similarly, some seedpods are stout, while some others are slender. While some capsules are oval shaped, there are other that distinctly exhibit their three sections. Again, seedpods of a number of iris species are fully ridged.
Even the seeds of irises vary greatly. They may have a smooth or coarse surface, while some may have a loose, glossy external layer. The seeds produced by aril irises, which includes Hexapogon, Regelias and Oncocycluses irises, have plump, creamy-white hued attachments at one end.
History of irises
Irises in the garden
Propagation of irises
Landscaping with irises
Pests of irises
Diseases of irises