Handel’s Xerxes is a green opera. In the Houston Grand Opera production, with its brilliant direction from Nicholas Hytner, sets and costumes by David Fielding and lighting design by Paul Pyant, “green” emerges both literally and figuratively. Most of the scenes are realized in vivid Kiwi-splash gardens and chambers, with only a few very small accents of purple and red.

In the opening scene, Xerxes, King of Persia, sings passionately of his love for a tree. A parade of plant life follows in the two remaining acts, from crooked cacti to towering hedges to placid palm trees, but the references are more than simple metaphors. I think Hytner and his artistic colleagues chose plants, and the essence of green at large, because it makes sense. Musically this epic work reaches out in all directions like an unruly rhizome. It’s without doubt organic.

With a runtime of 3 hours 40 minutes (including two hurried intermissions; you sure can’t miss those chimes at the Wortham), this might seem like an unsustainable concept. However, green is the foundation upon which a wider variety of more subtle ideas grow. Hytner has given all the characters of royalty or the military — the principal roles — great distinction through vivid blocking and slapstick. Xerxes topples statuary, Romilda slaps her lover, Atalanta beats her with a program, Elviro hobbles along disguised as an old woman selling flowers; these are busy and determined characters.

Juxtaposed against their varied action is a strangely robotic chorus of servants, soldiers and passersby, most of them in clown-white make-up and beige dress. And for those of you who have read up on the history and know that this opera was far ahead of its time when it premiered in 1738 (and flopped), what you might not have heard is just how much gender is in flux. The title role of the king is for a soprano, the lamenting yet macho Arsamenes is a counter-tenor singing in the soprano range, Amastris disguises herself as a man throughout most of the opera, and Elviro is a man pretending to be a woman yet sometimes singing like a man. This was way before Victor Victoria or Rent, and it's an endlessly fascinating narrative in Handel’s playful imagination.

For better or worse, it’s often my habit at the opera to discern which artists are the authentic stars and which ones are the “budget” singers and/or unknowns. I can’t do that this time around, because this is a perfect cast filled with great talent. I had heard that Susan Graham, in the title role, wasn’t feeling great on Sunday afternoon, but it wasn’t evident in her performance. She demonstrated astonishing skill and an enormous dynamic palette in her many arias. If she had to crash later at her hotel, she certainly deserves it.

The surprise was Italian contralto Sonia Prina, making her Houston Grand Opera debut as Amastris. As she struggles for recognition from Xerxes through the three acts, her arias become more and more florid, and this is a voice of brilliant power and nuance; I hope she will be back. Laura Claycomb is a fiery Romilda, and Heidi Stober a great comic artist as Atalanta. Adam Cioffari as Elviro is charismatic if not flamboyant, as if he’s sung the part for years.

With only a few arias, Philip Cutlip as Ariodates used his time wisely, with nearly show-stopping vocal prowess, and David Daniels a role-defining counter-tenor in this production. There is hardly any ensemble singing throughout, save for a few choral passages, and this gives the listener a great opportunity to closely examine each and every stellar voice.