Definite article vs. no article in front of plant names used generically

Question

There's a rule that when we use a noun generically, we either put the definite article in front of it or use the plural form:

1. The tiger is in danger of becoming extinct.
2. Tigers are in danger of becoming extinct.

However, I applied this rule to plant names in one of my posts on Lang-8, and it didn't work. Here's a native speaker's correction; marked with an underscore is the place I had originally put the definite article.

In contrast, a compound called myrcene, abundant in _ dill and wild rosemary, was harder for bees to pick up.

I've already seen this omission before. You could google, for example, the Wikipedia article about garlic mustard — it doesn't use any articles in front of the species name.

Why is it so? Is there no article because it's considered a proper name of sorts? Why doesn't that work in the tiger example, then?

Answer 1

This is a rather complicated issue. Your examples are from M.Swan's PEU, aren't they? But look how Geoffrey Leech and Jan Svartvik in A Communicative Grammar of English treat it:

The also has a generic use, referring to what is general or typical for a whole class of objects.This is found with count nouns: The tiger is one of the big cats; it is rivalled only by the lion in strength and ferocity. [1] Here the tiger indicates tigers in general, not one individual. Thus [1] expresses essentially the same meaning as [2] and [3]: Tigers have no mane. [2] A tiger has no mane. [3]

[2] is the generic use of the indefinite plural form; [3] is the generic use of the indefinite singular.

When we are dealing with a whole class of objects as here, the differences between definite and indefinite, singular and plural, tend to lose their importance. But there is a slight difference in the fact that the tiger (generic) refers to the species as a whole, while a tiger (generic) refers to any member of the species. We can say:

The tiger is in danger of becoming extinct.

Tigers are in danger of becoming extinct.

BUT NOT : *A tiger is in danger of becoming extinct.

I'm not a native speaker, so it's rather puzzling to me too.

Answer 2

If the noun is a count noun, we can refer to it generically either in the plural or with the definite article:

The tiger is endangered.

Tigers are endangered.

If the noun is non-count, we can refer to it generically without an article:

Dill grows wild in this area.

The compound myrcene is found in dill and rosemary.

Note, however, that we can cast a non-count noun as a count-noun when the situation requires:

Some varieties of dill are more pungent than others. These more pungent dills are often used in pickling.