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Classifying vegetables

Assorted summer vegetables - onions, sweet corn, tomatoes, beans, etc.

 

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.

 Harvested beetroot var. Boltardy in a trug Chiliies (Capsicum annuum) var. Joe E. Parker Sweet corn (Zea mays) var. Mainstay

Plants are given a genera and species name, hence beetroot is Beta vulgaris; 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.

Courgette var. Defender French beans

Courgettes and French beans are warm season crops that thrive in British summers.

Apero tomatoes Mini cucumbers Chilli var. Super Chile

... but some – like tomatoes, cucumbers and chillies – 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.

 

Broadbeans in the snow 

Broadbeans are cool season crops that tolerate British winters.

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.

Coriander var. Santos basil var. Sweet Genovese

Coriander and basil are short-term annuals.

 

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.

 carrots Perpetual Spinach

Carrots and perpetual spinach are biennials.

 parsley  Parsley in flower

Parsley is also a biennial: producing a continuous leaf crop in its first year, then flowers in its 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.

Globe artichokes Close up of globe artichoke 

Globe artichokes are perennials.

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.

four varieties of beetroot

Four different beetroot 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.

Pea var. Carouby de Maussane flower French bean var. Cobra

Pea (left) and French bean (right) flowers need no help to set fruit.

 

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.

brassicas are open pollinated  Purple Sprouting brocoli flower

White (left) and purple (right) sprouting broccoli in flower; brassica seeds are produced by cross-pollination

 

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.

Bumble bee with pollen on body

Insects move pollen from one plant to another, facilitating cross pollination.

 

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.

Ailsa Craig onions is a heritage variety 

Ailsa Craig onion still performs well in the garden.

 

 

Further reading

Deppe, C. 1993. Breed your own vegetable varieties: Popbeans, purple peas and other innovations from the backyard garden. Little, Brown and Company. ISBN no. 0-316-18104-8.

Bleasdale, J.K.A., Salter, P.J. and others.1991. The Complete Know and Grow Vegetables. Oxford University Press. ISBN no. 0-19-286114-X

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© Michael Michaud