Is the word espinafres the same in Brazilian and European Portuguese?

No

The difference lies in typical usage and grammar. In Brazil, the vegetable is almost exclusively referred to in the singular form: espinafre. While a Brazilian would understand "espinafres," it sounds distinctly European and unnatural in a daily context. In Portugal, it is standard and much more natural to use the plural form, espinafres, when referring to the leafy green.

Brazilian Portuguese Examples

1. Eu gosto de comer espinafre no café da manhã. (I like to eat spinach for breakfast.)
2. Você comprou espinafre no mercado? (Did you buy spinach at the market?)
3. O espinafre é muito saudável. (Spinach is very healthy.)
4. Vou fazer uma omelete de espinafre. (I'm going to make a spinach omelet.)
5. Tem um pouco de espinafre na salada. (There is a bit of spinach in the salad.)

Continental Portuguese Examples

1. Eu gosto de comer espinafres ao pequeno-almoço. (I like to eat spinach for breakfast.)
2. Compraste espinafres no mercado? (Did you buy spinach at the market?)
3. Os espinafres são muito saudáveis. (Spinach is very healthy.)
4. Vou fazer uma omelete de espinafres. (I'm going to make a spinach omelet.)
5. Há um pouco de espinafres na salada. (There is a bit of spinach in the salad.)