Plants Introduced by Romans

Centuries before conquering Britain, the Romans acquired plants from within their extensive empire. The archaeobotanical records of Roman Britain provide evidence that some of these species found their way to Britain when the Romans introduced fifty new plant foods. Some species were imported for consumption, others were introduced as crops, ornamentals, herbs, and fruit trees wherever Britain’s climate proved suitable for cultivation.

Preservation in the archaeological record depends upon favourable characteristics—hard seeds, and pips, and nut shells that resistant decay. Conversely, a species might have been present without leaving any trace.

The use of some herbs—coriander, poppy, celery, dill, and summer savory—increased during the occupation, only to fall out of fashion and favour after the decline of Roman influence between 383 and 410 CE.

Plants imported, introduced, and favoured by Romans: (w) indicates native wild form prior to Romans, (in) indicates probably introduced, (?) indicates that internet sources differ:

Cereals: wheat was grown in Britain for many years before the Romans introduced more productive strains and new grains: einkorn and millet.

Vegetables: garlic, onion, leaf beet (w), rape, cabbage (?w), turnip (? in), radish, leek, cucumber, carrot (w), parsnip (w), lettuce, asparagus (w), chicory (?)

Pulses: lentil, pea, bitter vetch, broad bean (?)

Fruits and berries: Fig, grape (possibly already introduced by the Belgae), mulberry, olive, peach, date, pomegranate, apple (w) + (in), pear, sweet cherry (w), sour cherry, cherry plum, plum, damson 

Nuts: walnut, pine nut, almond, sweet chestnut

Herbs, condiments, and medicinals : parsley, sage, rosemary, thyme, bay, savory mint, black pepper, coriander, dill, fennel (in), anise, summer savory, winter savory (?), black cumin, rue, white mustard, lovage, marjoram (w) celery (w), mint (w), horehound (w), borage (?), hyssop (?), marshmallow (?) 

Oil-rich seeds: sesame, gold of pleasure, hemp, poppy, black mustard

Other: hop (w), box tree (? in)

Vegetables regarded as weeds:
ground elder, Aegopidum podagraria
white mustard, Sinapis alba
alexanders, Smyrnium olasatrum (used as substitute for pepper)

Several foods (A) failed to become established, others (B) fell out of favour, and several (C) increased over time, becoming established.

Fruits

A Decreasing                                     fig, grape, mulberry
B Increasing/Decreasing                 olive, apple/pear
C Increasing                                      sweet/sour cherry, plum, bullace plum

Nuts

A Decreasing                                     –
B Increasing/Decreasing                 pine nut
C Increasing                                      walnut

Herbs

A Decreasing                                     –
B Increasing/Decreasing                 coriander, celery, dill, mint, summer savory
C Increasing                                      –

Vegetables

A Decreasing                                     –
B Increasing/Decreasing                 turnip, parsnip
C Increasing                                      carrot, leaf beet, cabbage


                                                            Pulses

A Decreasing                                     lentil
B Increasing/Decreasing                 –
C Increasing                                      –

Tabulated: Taxonomic list of Roman-introduced plants.

Sources: 

New Plant Foods in Roman Britain — Dispersal and Social Access, by Marijke van der Veen, Alexandra Livarda and Alistair Hill (pdf online)

Also:
Not all of these root vegetables were introduced by the Romans, but the article includes some interesting history of the development of root vegetables: ROOT VEGETABLES: UNSUNG HISTORICAL HEROES .

Geography of Spices & Fruits