Sub quercubus avia glandes numerat et dicit ex glandibus novam quercum nasci posse.

Here sub means under in the sense of location, so it takes the ablative case. Thus sub quercubus means under the oak trees or beneath the oaks.

A useful rule is:

• sub
  • ablative = being under something
• sub
  • accusative = motion to a place under something

So if someone were moving to a place under the trees, Latin could use the accusative instead.

Quercubus is an ablative plural form of quercus, meaning oak or oak tree. This noun belongs to the fourth declension, and some fourth-declension nouns use -ubus in the dative/ablative plural.

So quercubus is a real and correct form, not a typo.

Avia is the subject of both numerat and dicit. It is nominative singular feminine and means grandmother.

So the basic structure is:

• avia numerat = the grandmother counts
• avia dicit = the grandmother says

Latin often states the subject once and lets it apply to more than one verb.

Glandes is accusative plural, the direct object of numerat. It answers the question what is the grandmother counting? She is counting acorns.

The dictionary form is glans, glandis, and the accusative plural is glandes.

The preposition ex means out of or from, and it takes the ablative case. So glandibus is ablative plural.

Thus:

• ex glandibus = from acorns / out of acorns

This phrase shows source or origin: the new oak comes from acorns.

Both are present indicative active, third person singular:

• numerat = she counts
• dicit = she says

The subject is singular (avia), so the verbs are singular too.

After verbs of saying, thinking, knowing, and similar verbs, Latin often uses an accusative + infinitive construction instead of a clause with that.

So:

• dicit = she says
• novam quercum ... nasci posse = that a new oak can grow

Latin does not need a separate word for that here. The structure itself shows indirect statement.

A very literal unpacking would be something like:

• she says a new oak to be able to grow from acorns

But natural English is:

• she says that a new oak can grow from acorns

Because in this kind of indirect statement, the subject of the infinitive is put in the accusative case.

So in direct form, you might think of:

• nova quercus nascitur = a new oak grows / is born

But after dicit, Latin changes the subject into the accusative:

• dicit novam quercum nasci posse = she says that a new oak can grow

So novam quercum is the accusative singular of nova quercus.

Nasci is the present infinitive of nascor. It is a deponent verb, which means it has passive-looking forms but an active meaning.

So although nasci looks passive, it means something active like:

• to be born
• to arise
• to spring up
• to grow

With plants and trees, nasci is very naturally understood as to grow or to spring up.

Because posse means to be able, and it normally takes another infinitive to complete its meaning.

So:

• nasci = to grow
• posse = to be able

Together:

• nasci posse = to be able to grow

This is exactly like English can grow or to be able to grow.

By English standards, yes; by Latin standards, not really. Latin word order is much freer because the endings show each word’s role.

This sentence places important verbs and infinitives toward the end:

• numerat
• dicit
• nasci posse

That is very normal Latin style. The meaning depends mainly on case endings, not on rigid word order.

So even though English would normally say The grandmother counts acorns under the oaks and says that a new oak can grow from acorns, Latin can arrange the words more flexibly without becoming unclear.