Classifying vegetables - Sea Spring Seeds

Vegetables were once the second class citizens of the gardening world, ranking below fruit, flowers and shrubs in the hierarchy of plants. This is no longer the case; interest in healthy eating is on the increase and the pleasures of own-grown vegetables has become better appreciated.

Order from Chaos

In British gardens there are about 30 or so well-known vegetables and about ten commonly-grown herbs, with numerous minor crops thrown in for good measure (see table below). Though novice gardeners may be confused by such a jumble of plants, there are various classification schemes that bring order to all the chaos.

Scientific classification

In a branch of botany called taxonomy, plants with similar characteristics are grouped together into families (see table below). An understanding of these family relationships is more than just an intellectual exercise. The same pests and diseases often attack members of the same family so plant families lie at the heart of rotation designs.

Taxonomists then divide each family down into smaller groups called ‘genera’, with plants in each genus sharing certain traits that distinguish them from other genera. Genera are then divided into ‘species’, each of which has its own special characteristics. Using this system, beetroot belongs to the genus “Beta” and has the species name of ‘vulgaris’, hence beetroot’s scientific name is Beta vulgaris. Likewise, peppers are Capsicum annuum, and sweet corn is Zea mays.

Table: Family Connections

Plant family name	Previous name	Commonly grown vegetables and herbs	Less common vegetables and herbs
Alliaceae	Amaryllidaceae	Leek, Onion, Shallot	Chives
Apiaceae	Umbelliferae	Carrot, Coriander, Parsley, Parsnip	Celeriac, Celery, Fennel
Asteraceae	Compositae	Lettuce	Chicory/Endive, Globe artichoke, Jerusalem artichoke, Salsify, Scorzonera
Brassicaceae	Cruciferae	Broccoli/Calabrese, Brussel sprouts, Cabbage, Cauliflower, Kale, Chinese cabbage, Pak choi, Radish, Swede, Turnip	Kohlrabi, Texsel greens, Mizuna, Tatsoi
Chenopodiaceae		Beetroot, Perpetual spinach, Spinach	New Zealand spinach
Cucurbitaceae		Cucumber, Courgette	Pumpkin, Squash
Fabaceae	Leguminosae	Broad Bean, French Bean, Runner Bean, Pea	Fenugreek
Lamiaceae	Labiatae	Basil, Marjoram, Mint, Oregano, Rosemary, Thyme, Sage
Liliaceae			Asparagus
Poaceae	Gramineae	Sweet corn	Lemon grass
Solanaceae		Pepper, Potato, Tomato	Aubergine, Tomatillo

Temperature preference

Based on their temperature preference and cold tolerance, vegetables and herbs can be divided into either warm season or cool season crops. Both types are commonly grown in Britain, and a mix of each ensures diversity in the garden while extending its production potential.

Warm season crops thrive in the summer heat and are easily injured or killed by frost. They include among their numbers French beans and courgettes, while others, such as peppers and cucumbers, are partial to the extra warmth of a tunnel or greenhouse.

Alternatively, cool season crops can germinate and grow at cooler temperatures. Some tolerate the cold more than others, and the hardiest ones such as some kales, leeks and broad beans survive a typical British winter.

Flowering times

A plant’s life cycle starts with seed germination, then goes through a growth stage when leaves and stems are produced. This is followed by a reproductive stage characterised by the production of flowers and seeds, after which the plant finally dies. Vegetables and herbs are classified either as annuals, biennials or perennials based on the duration of their life cycles.

Annuals run through their life cycle within one growing season. Short-lived crops, like coriander, radish and lettuce, flower and go to seed very quickly, and to have a continuous harvest gardeners have to do succession sowings. In contrast, others such as climbing French beans, have an extended flowering and fruiting period that can last throughout the summer and into the autumn.

Biennials flower, seed and die in their second season. Some leafy biennials, like parsley and perpetual spinach, are harvested for their leaves throughout their first year, finally stopping when they flower in the spring of the following year. Other crops such as carrots and onions are also biennial, though in the vegetable garden they are treated as annuals and harvested in the first year of their life. However, if left growing they would flower in their second year.

Perennials such as globe artichokes and rosemary live for a number of years before succumbing to the ravages of old age. Botanically, runner beans, peppers and tomatoes are also perennials, though in cold northern gardens, they die each year as if they were annuals.

Varieties

A ‘variety’ in gardening terms is a group of plants within a species that is distinguished by certain characteristics like size and colour. The red ‘Crimson Globe’ beetroot, for example, differs in colour from the yellow ‘Burpee’s Golden’. Both are obviously beetroots, yet have traits that separate them into two different varieties.

The seeds of different varieties are produced differently, depending on the reproduction method of the plants and the amount of effort the breeder is willing to donate. In general, the vegetable varieties in the seed catalogues fall into 3 broad categories.

Self-pollinated or self-fertilised varieties

Self-pollination or self-fertilisation occurs when a plant sets seeds with its own pollen. In cases where this is the usual method of reproduction, the plant is called an inbreeder.

Some self-pollinators, like French beans and peas, need no outside intervention for their flower to set fruit. Runner beans are also self-pollinators but their flowers need the help of bees visiting the flowers for pollination to take place.

Plants of inbreeders can also cross-pollinate among themselves, usually by the action of bees. This isn’t a problem for the home gardener, who just wants to produce a crop. However, cross-pollination does have serious implications for the seed producer, who must keep varieties of the same species separate in order to maintain the genetic purity of the crop.

Cross-pollinated varieties

The seeds of vegetables such as brassicas, onions and carrots are produced by cross-pollination. Though some seed results from self-fertilisation, this is usually only a small part of the total amount.

When cross pollination occurs, it is usually facilitated by insects moving pollen from one plant to another. There are exceptions, and in some vegetables such as sweet corn and beetroot, the plants are cross-pollinated by the wind.

Open pollinated vs hybrid varieties

Hybrid varieties:

A relatively modern phenomenon, hybrid varieties are a product of two pure-bred lines that are crossed with each other. Such a cross produces seed designated as an ‘F1 hybrid’. Hybrid breeding is generally more costly than traditional breeding methods, which means that seed is often more expensive to buy. In addition, any seed collected from a hybrid variety will not come back true-to-type.

Hybrids tend to produce high quality, uniform crops, that generally have good pest and disease resistance. Despite their expense, however, they have much to offer the home gardener and represent value for money.

Open pollinated varieties:

Open pollinated (OP) varieties are produced from so called traditional breeding methods. Their populations are more variable than those of hybrid varieties, but remain stable from one generation to the next.

Today’s breeders still use traditional techniques to produce new OP varieties. However, older varieties, such as Ailsa Craig onion, still perform well in the garden and shouldn’t be abandoned completely. The best gardens are probably those using a mix of old and new, as well as hybrid and OP varieties.