Three estranged siblings, one vegetative father and a nine-year burden that's tearing a couple apart: Venezuelan playwright Cesar Sierra packs a lot of drama into his 80-minute dark comedy "La Lechuga." Under these stars, emotions could certainly be expected to run high. But in Teatro de la Luna's season-opening production, it's often difficult to tell whether the histrionics onstage are meant to make you laugh or cry.

Every year the Martinez children -- who otherwise don't speak -- gather for their dad's birthday even though he's been brain-dead and hooked to a respirator for nearly a decade (lechuga means lettuce). The "celebrations" are always contentious, but this time there's something extra to fight about: Hector (Mario Marcel) and wife Virginia (Nucky Walder) have been caring for her father since he got sick, but now Hector wants one of Virginia's brothers to relieve them.

When both the flamboyant Vinicio (Peter Pereyra), citing his singleness, and the bitterly married Victor (Oscar Ceville), noting his six kids with another on the way, scoff at the idea, everyone butts heads until a morally questionable decision is made.

Though the wide age range of the actors playing the siblings stretches credibility a bit, Teatro's cast members cut sharp characters in "Lechuga's" two brief acts, especially Marcel's matter-of-fact brother-in-law, Ceville's browbeaten family man and Anabel Marcano's Dora, the pregnant and controlling wife of Victor. Pereyra and Walder are less successful in their roles, but largely because the parts aren't well defined: Vinicio unrealistically vacillates between flippant and a more serious, wounded personality, while Virginia seems meant to be the heart of the play, but more often simply supplies the hysteria.

And hysteria is something director Harold Ruiz amps up in this production, usually to slapstick effect. The characters jump atop tables, flail their arms and try to outyell each other, and though the chaos is at times mildly funny, the gravity of the underlying argument doesn't lend itself to wackiness.

Especially since Sierra's script, while offering the occasional joke ("What if we raffle him?"), more strongly highlights the family's divisiveness: In addition to dredging up old grievances, the characters, if only for the sake of extra conflict, point out a rather unbelievable new one -- that Virginia and Hector's 12-year-old "Chinese midget" son is clearly adopted. Seems like a topic that would have been broached before, and though the detail is minor, it adds to the feeling that much of "Lechuga's" emotion is either forced or misplaced.

Sierra's brisk story also loses momentum under Teatro's dramatic flourishes, including lights that go up and down too frequently -- and arbitrarily -- and odd musical interludes, one of which suggests an unlikely flirtation between Dora and Vinicio. During this short scene, Dora gets drunk and tells her brother-in-law, "I don't know what I'm laughing at, but it's so amusing!" Judging by the audience's uncertain titters during a recent performance, the first half of that line may offer "La Lechuga's" most relatable sentiment.

La Lechuga, by Cesar Sierra. Directed by Harold Ruiz. Set, Mario Marcel; lighting, Ayun Fedorcha; sound, Harold Ruiz; costumes, Nucky Walder. Approximately 80 minutes. Through Nov. 13 at Gunston Arts Center Theater II, 2700 S. Lang St., Arlington. Call 703-548-3092 or visit www.teatrodelaluna.org.

From front, Nucky Walder, Peter Pereyra and Oscar Ceville are siblings at odds over their comatose father in Teatro de la Luna's "La Lechuga."