A Vocabulary Precise Enough to Describe Any Flower

Pull any weed out of the ground and it will show you the same basic plan every flowering plant shares: a root system below the soil and a shoot system above it. In most dicotyledonous plants, the radicle itself elongates directly into a primary root that grows down into the soil and branches into secondary and tertiary roots, together forming a tap root system, mustard being a typical example. In monocotyledonous plants the primary root is short-lived and gets replaced by a large number of roots arising from the base of the stem, forming a fibrous root system, as in wheat. In some plants, grass, Monstera and the banyan tree among them, roots arise from parts of the plant other than the radicle entirely and are called adventitious roots. Roots absorb water and minerals, anchor the plant, store reserve food, and synthesise plant growth regulators. Just above the protective, thimble-like root cap sits the region of meristematic activity, where small, thin-walled, densely protoplasmic cells divide repeatedly; the region of elongation just above that is where cells enlarge rapidly, driving growth in length; and the region of maturation beyond that is where cells differentiate, some epidermal cells there forming the fine, thread-like root hairs that do the actual work of absorbing water and minerals.

The stem is the ascending part of the axis, developing from the plumule, bearing branches, leaves, flowers and fruits; it carries nodes, where leaves are born, and internodes, the stretches between them, and it also bears terminal or axillary buds. Beyond spreading out the plant's photosynthetic and reproductive parts, stems conduct water, minerals and photosynthates, and in some plants store food, provide support, or enable vegetative propagation. The leaf, a lateral, usually flattened structure borne at a node with a bud in its axil, consists of a leaf base, petiole and lamina, the flat green blade veined for both rigidity and transport, with a prominent central midrib. When the veinlets of the lamina form a branching network, the venation is reticulate, typical of dicots; when the veins instead run parallel to each other, the venation is parallel, typical of monocots. A leaf is simple when its lamina is either entire or incised without the incisions reaching the midrib; when the incisions do reach the midrib, breaking the blade into separate leaflets, the leaf is compound, either pinnately compound, with leaflets along a common central rachis as in neem, or palmately compound, with leaflets all attached at one point at the tip of the petiole as in silk cotton. The arrangement of leaves on the stem, called phyllotaxy, is typically alternate, one leaf per node as in china rose and mustard, opposite, a pair per node as in guava, or whorled, more than two leaves per node as in Alstonia.

A flower is, structurally, a modified shoot: the shoot apical meristem transforms into a floral meristem, internodes stop elongating, the axis condenses, and the apex produces floral appendages laterally instead of leaves. The arrangement of flowers on the floral axis is called inflorescence, and depending on whether the apex itself develops into a flower or keeps growing, two major types result. In racemose inflorescences the main axis keeps growing indefinitely, with flowers borne laterally in acropetal succession, the youngest nearest the growing tip. In cymose inflorescences the main axis itself terminates in a flower, limiting its own growth, with flowers instead borne in basipetal order. When a shoot tip transforms directly into a flower without any inflorescence structure at all, the flower is solitary.

A typical flower carries four different kinds of whorls arranged successively on the thalamus, the swollen end of the pedicel: calyx and corolla, the accessory organs, and androecium and gynoecium, the actual reproductive organs. Some flowers, lily among them, don't distinguish calyx from corolla clearly, and the combined whorl is then called a perianth. A flower with both androecium and gynoecium is bisexual; one with only stamens or only carpels is unisexual. Symmetry offers a second, independent way to describe a flower: actinomorphic when it can be divided into two equal halves along any radial plane through the centre, as in mustard, datura and chilli; zygomorphic when it can be divided into two equal halves only along one specific vertical plane, as in pea, gulmohur and bean; and asymmetric when no plane at all divides it evenly, as in canna. Flowers are also described by merosity, trimerous, tetramerous or pentamerous, when the floral appendages come in multiples of three, four or five, and by the presence or absence of bracts, reduced leaves at the base of the pedicel, bracteate flowers having them and ebracteate flowers lacking them.

Based on the position of calyx, corolla and androecium relative to the ovary on the thalamus, flowers are described as hypogynous, perigynous or epigynous. In hypogynous flowers the gynoecium sits at the very top, with the other whorls below it; the ovary here is superior, as in mustard, china rose and brinjal. In perigynous flowers the gynoecium sits centrally with the other parts arranged around the rim of the thalamus at roughly the same level; the ovary is half-inferior, as in plum, rose and peach. In epigynous flowers the margin of the thalamus grows upward, enclosing the ovary completely and fusing with it, so the other parts arise above the ovary; the ovary here is inferior, as in guava, cucumber and the ray florets of sunflower. Within the calyx, sepals may be gamosepalous, united, or polysepalous, free; within the corolla, petals may be similarly gamopetalous or polypetalous, and corolla shape varies from tubular to bell-shaped to funnel-shaped to wheel-shaped. The arrangement of sepals or petals within a bud relative to each other, called aestivation, comes in four recognised patterns: valvate, where members just touch at the margin without overlapping, as in Calotropis; twisted, where each margin overlaps the next in sequence, as in china rose and cotton; imbricate, where margins overlap without a fixed direction, as in Cassia and gulmohur; and vexillary, unique to flowers like pea and bean, where the largest petal, the standard, overlaps two lateral wing petals, which in turn overlap the two smallest keel petals.

The androecium, composed of stamens, is the male reproductive whorl; each stamen consists of a filament and an anther, usually bilobed with two chambers per lobe called pollen sacs, where pollen grains are produced, and a sterile stamen is called a staminode. Stamens may be attached to petals, epipetalous, as in brinjal, or to a perianth, epiphyllous, as in lily; they may remain entirely free, polyandrous, or fuse in varying degrees, into one bundle, monoadelphous, as in china rose, two bundles, diadelphous, as in pea, or more than two, polyadelphous, as in citrus. The gynoecium, the female reproductive part, is made up of one or more carpels, each consisting of stigma, style and ovary; the ovary is the enlarged basal part bearing ovules attached to a placenta, the style connects the ovary to the stigma, and the stigma is the receptive surface for pollen. When more than one carpel is present, they may remain free, called apocarpous, as in lotus and rose, or fuse together, called syncarpous, as in mustard and tomato. The arrangement of ovules within the ovary is called placentation, and comes in several recognised types: marginal, where the placenta forms a ridge along the ventral suture bearing ovules in two rows, as in pea; axile, where the placenta is axial in a multilocular ovary, as in china rose, tomato and lemon; parietal, where ovules develop on the ovary's inner wall, the ovary appearing two-chambered due to a false septum, as in mustard; free central, where ovules sit on a central axis with no septa, as in Dianthus; and basal, where the placenta develops at the ovary's base bearing a single ovule, as in sunflower.

The fruit, a feature unique to flowering plants, is the mature or ripened ovary that develops after fertilisation; if a fruit forms without fertilisation at all, it is called parthenocarpic. The fruit generally consists of a wall, the pericarp, which may be dry or fleshy, and seeds; when thick and fleshy, the pericarp differentiates into an outer epicarp, a middle mesocarp and an inner endocarp. In mango and coconut, both drupes developing from a single-carpelled superior ovary, the pericarp is clearly layered: in mango into a thin epicarp, a fleshy edible mesocarp and a stony endocarp; in coconut the mesocarp is instead fibrous. After fertilisation ovules develop into seeds, each seed made up of a seed coat and an embryo, the embryo itself consisting of a radicle, an embryonal axis, and either one cotyledon, as in wheat and maize, or two, as in gram and pea. A dicotyledonous seed's outer covering, the seed coat, has an outer testa and inner tegmen, with a hilum scar marking where the seed once attached to the fruit and a micropyle pore just above it; within lies the embryo with its two often food-storing cotyledons, radicle and plumule; some dicot seeds, castor among them, retain a food-storing endosperm formed by double fertilisation and are called endospermic, while others, like bean, gram and pea, consume that endosperm entirely during development and are non-endospermous. A monocotyledonous seed, generally endospermic, has a membranous seed coat usually fused to the fruit wall, a bulky food-storing endosperm separated from the embryo by a proteinous aleurone layer, and a small embryo bearing a single shield-shaped cotyledon called the scutellum, with its plumule and radicle each enclosed in a protective sheath, the coleoptile and coleorhiza respectively.

Every technical term built up across this chapter exists for one purpose: describing a plant precisely enough that a floral formula and floral diagram can capture it completely. The floral formula uses standard symbols, Br for bracteate, K for calyx, C for corolla, P for perianth where calyx and corolla aren't distinct, A for androecium, G for gynoecium, a line above symbols for adhesion, brackets around a number for fusion, and separate symbols for superior ovary, inferior ovary, actinomorphic, zygomorphic, and unisexual or bisexual flowers. A floral diagram, meanwhile, shows the number of parts in each whorl, their arrangement and their relation to one another, with the mother axis marked by a dot at the top and the four whorls drawn in successive rings, calyx outermost and gynoecium at the centre. The family Solanaceae, widely known as the potato family and distributed across tropics, subtropics and temperate zones, demonstrates the whole system in practice: herbs, shrubs or rarely small trees, with alternate simple leaves and reticulate venation; solitary or cymose inflorescences; bisexual, actinomorphic flowers with five united sepals, five united petals, five epipetalous stamens, and a syncarpous, bicarpellary, superior, bilocular ovary with axile placentation, producing berries or capsules as fruit. This single family alone supplies food, in tomato, brinjal and potato, spice, in chilli, medicine, in belladonna and ashwagandha, tobacco, and ornamentals like petunia, all describable, precisely and completely, in one line of floral formula.