O rebento murchou; isso é um facto.

Here, rebento means a shoot, sprout, or new plant growth. It is a botanical word.

Be aware that rebento can also mean child or offspring in other contexts, so the exact meaning depends on what is being talked about. In this sentence, because it murchou (withered), it clearly refers to a plant shoot.

O is the masculine singular definite article, so o rebento means the shoot or the sprout.

Portuguese uses articles more often than English does. In many contexts, a noun sounds more natural with an article, especially when referring to a specific thing already known in the situation.

So:

• o rebento = the shoot
• um rebento = a shoot

Murchou is the 3rd person singular of the pretérito perfeito simples of murchar.

That means it expresses a completed past action:

• murchar = to wither / to wilt
• murchou = it withered / it wilted

In this sentence, it presents the withering as a finished fact.

Compare:

• O rebento murchou. = The shoot withered.
• O rebento está murcho. = The shoot is withered / wilted.

The first focuses on the event; the second focuses on the resulting state.

Portuguese often leaves out subject pronouns when the verb form already makes the subject clear. This is very normal.

So instead of saying:

• Ele murchou

Portuguese can simply say:

• Murchou

In your sentence, the subject is already stated as o rebento, so there is no need to repeat it.

Isso means that, and here it refers back to the whole previous statement: O rebento murchou.

So:

• O rebento murchou; isso é um facto.
• The shoot withered; that is a fact.

This is a very common use of isso in Portuguese: referring to an idea, statement, or situation just mentioned.

A useful quick contrast is:

• isto = this
• isso = that
• aquilo = that over there / that yonder

In real usage, isso is often the natural choice for referring back to something someone has just said.

Because Portuguese normally uses an article with this kind of predicate noun.

So:

• é um facto = it is a fact

This is more natural than leaving the article out. English sometimes says it is fact in special structures, but Portuguese usually prefers um here.

Other similar examples:

• É um problema. = It is a problem.
• É uma pena. = It is a shame.
• É uma verdade. = It is a truth.

In European Portuguese, facto is the normal spelling for fact.

This is an important difference between Portugal and Brazil:

• Portugal: facto = fact
• Brazil: fato = fact

Also, in European Portuguese, fato usually means suit (clothes), not fact.

So for Portugal Portuguese, isso é um facto is exactly what you would expect.

Yes. The semicolon is used to connect two closely related independent clauses:

• O rebento murchou
• isso é um facto

It gives a slightly formal, careful written style.

You could also write:

• O rebento murchou. Isso é um facto.
• O rebento murchou, e isso é um facto.

The version with the semicolon sounds neat and quite formal in writing.

Yes. É um facto and isso é um facto are common ways to say that something is undeniably true.

They sound fairly neutral to slightly formal. Depending on context, English equivalents could be:

• that is a fact
• that’s a fact
• it’s a fact

In more everyday conversation, people might also say:

• É verdade. = It’s true.
• Isso é verdade. = That’s true.

So isso é um facto is perfectly natural, but a little more emphatic or formal than isso é verdade.

Usually, isso is the best choice here because it refers back to something just mentioned.

Very roughly:

• isto often points to something close to the speaker, or something the speaker is about to say
• isso often points to something near the listener, or something already mentioned
• aquilo points to something more distant

When referring back to the previous statement O rebento murchou, isso is the most natural option.

In European Portuguese, the c in facto is pronounced, which is one reason the spelling keeps the c.

A broad approximation is:

• facto ≈ FAK-too

But remember that European Portuguese pronunciation is often more reduced than English learners expect, especially unstressed vowels.

Also:

• murchou is pronounced roughly like moor-SHOH
• rebento is roughly reh-BEN-too in careful approximation

These are only rough guides. The real European Portuguese sound is more compact and less fully pronounced than English spelling-based approximations suggest.