Having I look at this website: http://www.fpepito.org/utils/conjugue.php?verbo=distinguir, the word "distinguam" in your example is correct. However, even the most natives speaking Portuguese would not know which is the correct, "distinguam" or "distinguem" in the day-to-day.

Yes, is a typo. You should write: "logo que se distingam das roseiras" Notes about the verbal forms in your question: - DISTINGAM: I think the correct form of the verb "distinguir" that better match your example is "distingam" (3rd person/plural of the subjuntivo/conjuntivo form). Because in your example, the action of "distinguir" of the baobás is not a certainty and the verbal form that expresses an hypothetical action is "subjuntivo/conjuntivo". - DISTINGUEM: It's the present form of the verb using the 3rd person/plural. You use this form to talk about an action related to the present moment performed by "they". For example: "Os melhores se distinguem pela qualidade do seu trabalho" - DISTINGUIAM: It's the "Pretérito Imperfeito" tense, also in the 3rd person/plural. Briefly, this tense expresses an usual routine action that happened in the past performed by "they". Example: "Naquele tempo, distinguiam muito pouco o que acontecia ao seu redor"

It's a typo or even a mistake, cause the verb "distinguir" is hard to be found in subjective form in contexts. "To distinguish" is more normally used in indicative form. "Ele não distingue a diferença" or "Eu distingo (without U) azul de roxo." "GU" only before "E" and "I". (y) See: http://www.conjugador.com.br/index.php?verbo=distinguir&pesquisa=1

Veja bem, esta é uma palavra importante. Quando não usamos "difere, é diferente" podemos usar "distingue". Aqui está a conjugação deste verbo em todos os tempos verbais (: http://www.conjuga-me.net/verbo-distinguir