Planta acvatică este în acvariu.

Because Romanian usually puts the definite article at the end of the noun instead of using a separate word like the.

• plantă = a plant
• planta = the plant

So in this sentence, planta is definite: it means a specific plant, not just any plant.

In Romanian, adjectives often come after the noun.

So:

• planta acvatică = the aquatic plant

This is the normal order in many Romanian noun phrases. English usually says adjective + noun, but Romanian very often prefers noun + adjective.

Because the adjective has to agree with the noun in gender and number.

Here, plantă / planta is:

• feminine
• singular

So the adjective also has to be feminine singular:

• masculine singular: acvatic
• feminine singular: acvatică

That is why the sentence uses acvatică.

The dictionary form is plantă, meaning plant.

Then Romanian adds the definite article to the end:

• plantă = a plant
• planta = the plant

You may also notice that the final sound changes when the article is added. This is a normal pattern with some feminine nouns.

In standard Romanian, you normally do use the verb a fi (to be) in sentences like this.

So:

• Planta acvatică este în acvariu. = The aquatic plant is in the aquarium/an aquarium.

Leaving out este would not be standard in this kind of sentence.

În means in or inside.

So:

• în acvariu = in an aquarium / in the aquarium, depending on context and article choice

It is a very common Romanian preposition.

Because acvariu is the indefinite form, while acvariul is the definite form.

• acvariu = an aquarium
• acvariul = the aquarium

So:

• în acvariu = in an aquarium
• în acvariul = in the aquarium

If your provided meaning uses the aquarium, then a learner might notice that Romanian would more explicitly say în acvariul for that. Without the definite article, în acvariu usually sounds more like in an aquarium.

Yes. This is the most neutral, standard order:

• Planta acvatică = subject
• este = verb
• în acvariu = place/location

So the pattern is basically:

Subject + is + location

This is very natural Romanian word order.

The letter ă is a very common Romanian vowel. It is a short, unstressed central sound, somewhat like the a in English sofa.

So roughly:

• plantă ≈ PLAN-tuh
• acvatică ≈ ak-va-TEE-kuh

That final ă is not a strong a sound like in father.

Yes, they are helpful cognates.

• plantă ≈ plant
• acvatic(ă) ≈ aquatic
• acvariu ≈ aquarium

So this sentence contains vocabulary that may feel familiar to an English speaker, even though the grammar works differently.

Yes, but it means something slightly different in structure.

• Planta acvatică este în acvariu. = The aquatic plant is in the aquarium/an aquarium.
• Planta este acvatică. = The plant is aquatic.

In the original sentence, acvatică is part of the noun phrase planta acvatică. In the second sentence, acvatică is a predicate adjective describing the plant through the verb este.

Usually, yes, in ordinary neutral Romanian.

• planta acvatică = the aquatic plant

Romanian can sometimes place adjectives before the noun for emphasis, style, or special meaning, but for learners, the safest and most natural choice is to put most descriptive adjectives after the noun.