I don't think this is a technical term. It's a metaphor comparing the shrubs and bushes that tend to accompany this tree to the entourage or retinue of an important personage on a ceremonial occasion. The relevant DRAE definition would be:
"Conjunto de personas que forma el acompañamiento en una ceremonia"
http://dle.rae.es/?id=B2D63JO

I think retinue is more usual with royalty and entourage with politicians. I think the metaphor works perfectly well in English; it gives a the text a bit of colour and it would be a pity to water it down. The idea is simply a group of minor entities supporting and emphasising the grandeur of a major entity. I think retinue of species is much more convincing as a metaphor than an entourage, and it sounds fine to me.

This is a description of a tree and surrounding plants. I think entourage could be suitable.
Pistacia atlantica, and an entourage of species of shrubs...

en•tou•rage
1. a group of attendants or associates, as of a person of rank or importance: The opera singer traveled with an entourage of 20 people.
2. surroundings; environment: a house with a charming entourage of trees and flowers.
3. Archit.the landscaping and other nearby environmental features shown on a rendering of a building.
http://dictionary.infoplease.com/entourage


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Note added at 2 hrs (2016-12-22 19:30:45 GMT)
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I've just read the explanations Charles wrote and his mention of entourage. Due to wifi issues I didn't notice that until after I had posted my suggestion.

My rendering