Στο φυτώριο βρήκαμε μελίγκρα, ένα παράσιτο των φυτών.

Στο is the contracted form of σε + το.

So:

• σε = in / at / to / on
• το = the for a neuter noun
• στο = in the / at the / to the

In this sentence, στο φυτώριο means at the nursery or in the nursery, depending on the context.

This contraction is very common in modern Greek:

• σε + το = στο
• σε + τη(ν) = στην
• σε + τον = στον

Το φυτώριο means a plant nursery or garden nursery: a place where plants are grown and often sold.

It does not mean a nursery for children here.

It is related to φυτό (plant), so that can help you remember it:

• φυτό = plant
• φυτώριο = plant nursery

Βρήκαμε is the 1st person plural aorist of βρίσκω (to find).

So it means we found.

Why the aorist?
Because the sentence presents the action as a single completed event.

Compare:

• βρήκαμε = we found
• βρίσκαμε = we were finding / we used to find

Greek often uses nouns like this in a more general or collective way than English does.

So βρήκαμε μελίγκρα can mean that aphid was found there as a pest problem, without focusing on counting individual insects.

That is why there is no μια here.

Compare:

• βρήκαμε μελίγκρα = we found aphid / aphids / aphid infestation
• βρήκαμε μια μελίγκρα = we found one aphid
• βρήκαμε μελίγκρες = we found aphids

So the sentence is focusing more on the type of pest than on the exact number.

The dictionary form is η μελίγκρα. It is a feminine noun.

Useful forms:

• η μελίγκρα = nominative singular
• τη(ν) μελίγκρα = accusative singular
• οι μελίγκρες = nominative plural
• τις μελίγκρες = accusative plural

In the sentence, μελίγκρα is the direct object of βρήκαμε, so it is functioning as an accusative.

Because ένα παράσιτο των φυτών is an apposition: it explains or renames μελίγκρα.

So the structure is:

• μελίγκρα, ένα παράσιτο των φυτών

This is like saying:

• aphid, a parasite of plants

The comma shows that the second phrase is extra explanatory information.

Because ένα agrees with παράσιτο, not with μελίγκρα.

• μελίγκρα is feminine
• παράσιτο is neuter

In apposition, both nouns refer to the same thing, but each noun keeps its own grammatical gender.

So:

• μελίγκρα = feminine noun
• ένα παράσιτο = neuter noun phrase

That is completely normal in Greek.

Των φυτών means of the plants.

Greek uses the genitive here to show the relationship, just as English uses of:

• παράσιτο των φυτών = parasite of the plants / plant parasite

Useful forms of φυτό:

• το φυτό = the plant
• τα φυτά = the plants
• των φυτών = of the plants

So των is the genitive plural definite article, and φυτών is the genitive plural of φυτό.

Here is the grammar of the main noun phrases:

• στο φυτώριο: after σε, Greek uses the accusative
• μελίγκρα: accusative singular, as the direct object of βρήκαμε
• ένα παράσιτο: also accusative singular, in apposition to μελίγκρα
• των φυτών: genitive plural

One thing that can confuse learners is that some forms look the same in nominative and accusative:

• το φυτώριο has the same form in nominative and accusative
• παράσιτο also looks the same in nominative and accusative
• μελίγκρα often looks the same in nominative and accusative singular too

So you have to identify the case from the sentence function, not only from the form.

Greek word order is more flexible than English word order.

Starting with Στο φυτώριο puts the location first and sets the scene:

• Στο φυτώριο βρήκαμε... = At the nursery, we found...

You could also say:

• Βρήκαμε μελίγκρα στο φυτώριο

That is also grammatical, but it gives a slightly different emphasis. The original sentence highlights where the finding happened first.