Apud la fenestro staras vazo kun verda planto, kiun mia amikino aĉetis hodiaŭ.

Esperanto word order is fairly flexible. Putting Apud la fenestro first gives the location first, and then staras vazo introduces what is there. It is a very common descriptive pattern, especially in scene-setting.

So vazo is still the subject, even though it comes after the verb. Vazo staras apud la fenestro is also correct, but the original sounds a bit more natural for introducing the scene.

In Esperanto, the subject does not have to come before the verb. The main clue is the ending: vazo has no -n, so it is not a direct object.

Also, the verb staras is intransitive here, so it does not take a direct object anyway. The sentence is saying that a vase is standing there, not that someone is standing a vase.

After a preposition like apud, Esperanto normally uses the basic noun form, not the accusative -n. So apud la fenestro means beside the window or by the window.

You only get -n after a preposition in special cases, usually when you want to show movement toward something. Here there is no movement; it is just location.

Stari means to stand, and Esperanto often uses position verbs very naturally with objects. A vase is thought of as an upright object, so staras paints a more vivid picture than plain estas.

If you said Apud la fenestro estas vazo, that would still be correct. It would just sound more neutral and less visual.

La is the definite article, so it marks something as specific or identifiable. La fenestro suggests a particular window that is already clear from context.

By contrast, vazo and planto are being introduced as new items: a vase and a green plant. That is why they appear without la.

Kun means with, so vazo kun verda planto means a vase with a green plant. The preposition kun is followed by a noun phrase in its normal form.

Verda ends in -a because it is an adjective, and it agrees with planto, which is singular. There is no -n here, because this phrase is not a direct object.

Kiun is the accusative form of kiu used as a relative pronoun, meaning who/which/that depending on context. The -n is there because inside the relative clause it is the direct object of aĉetis.

In other words, the structure is basically: mia amikino aĉetis kiun hodiaŭ → my friend bought which today. So even if the noun it refers to is not an object in the main clause, kiun gets -n because of its role inside the relative clause.

This is a good question, because the sentence is a bit ambiguous. Many readers will naturally connect kiun to the nearest sensible noun, planto, so they will understand the green plant that my friend bought today.

But grammatically, the wording can leave room for doubt, since vazo is also singular and could in principle be the thing bought. If you want to be completely clear, it is better to rephrase the sentence.

Amikino means female friend. The element -in- is the feminine suffix, so amiko is friend, and amikino is specifically a female friend.

Here mia amikino is the subject of aĉetis. That is why it stays in the basic form and does not take -n.

Yes. Hodiaŭ is an adverb meaning today, and Esperanto allows fairly flexible adverb placement.

In this sentence it modifies aĉetis, so kiun mia amikino aĉetis hodiaŭ means which my friend bought today. You could also say kiun mia amikino hodiaŭ aĉetis without changing the basic meaning.

In Esperanto, commas are commonly used to mark subordinate clauses, including relative clauses introduced by words like kiu, kiun, kie, and so on. So the comma before kiun is standard punctuation.

This is a little more regular than in English, where comma use with relative clauses depends more heavily on whether the clause is restrictive or non-restrictive. In Esperanto, learners should expect to see commas before these kinds of clauses quite often.