Some Russian words for fruits and vegetables that are collective, like English "bread." These don't have plurals except in special contexts, like when referring to more than one kind.
The suffix -ина is sometimes added to refer to a particular item. You can also use штука "item" to describe a counted number: пять штук вишин.
A diminutive suffix may also be added. See
this post on learn_russian where some Russian speakers comment on how they use the diminutive with these collective nouns.
брусн
ика cowberries
в
ишня cherries
гор
ох peas
ежев
ика blackberries
землян
ика wild strawberries
кап
уста cabbage
карт
офель (m) potatoes
клубн
ика cultivated strawberries
крыж
овник gooseberries
лук onions
мал
ина raspberries
морк
овь (f) carrots
кр
асная смородина redcurrants
чёрная смород
ина blackcurrants