The title page of da Silva’s opera Guerras do Alecrim e Mangerona (Wars of the Rosemary and of the Marjoram) bears the indication “ópera joco-séria”; this phrase refers to a serious form of comedy and has been applied to da Silva’s entire theatrical work. Performed during the Carnival of 1737 at the Bairro Alto theatre, Guerras do Alecrim e Mangerona is da Silva’s sixth comedy; it was again written for music by Antόnio Teixeira. Da Silva moved away from mythological motifs in this play; instead, he focused on contemporary Portuguese customs: the rosemary and the marjoram represent two clans which were most likely opposed during the Carnival – a time of the year which fostered competition. The play was printed by the typographer Antonio Isidoro da Fonseca on the year it was premiered; it was printed again later in a posthumous publication with da Silva’s other plays. This has been and remains his most performed play, in both Portugal and Brazil.

The libretto follows the pattern used by da Silva since Os Encantos de Medeia: a double love story between two romantic couples. Their story is paralleled by a couple of graciosos (comical valet and maid), who replicate their masters’ love affairs in a farcical mode. The plot is borrowed from baroque comedy, which is itself a legacy of ancient Rome comedy: an old miser, D. Lanserote, wants his daughters to marry rich but foolish men, or to enter a convent. D. Tibúrcio, like Molière’s Pourceaugnac, is duped several times by the gracioso.

Dom Gilvaz and Dom Fuas become enamoured with Dona Clóris and Dona Nise, the two nieces of the miser Dom Lanserote; Semicúpio, Dom Gilvaz’s servant, falls in love with their maid Sevadilha. Dona Nise gives her suitor a sprig of marjoram, Dona Clóris gives hers a sprig of rosemary and Sevadilha gifts hers a daisy; they encourage them to make these symbols triumph. The old Fagundes, Dom Lanserote’s maid, agrees to help the lovers. She reveals that one of the young women is promised to the foolish Dom Tibúrcio, and that the other will be sent to a convent. While Dom Tibúrcio is wooing Sevadilha, Semicúpio sneaks into the house; he is carrying a bundle of rosemary for Dom Gilvaz. When he faints, Fagundes sprays water on him and then leaves him with Sevadilha. The two servants bond; this ingenious couple will drive the action of the play. Dom Gilvaz catches Dom Fuas as he is climbing a ladder to break into the house: everyone enters the house and the two rivals, envying each other, engage in dialogues with their beloved. Dom Lanserote stops these outpourings. To escape this bad situation, Semicúpio claims that there is a fire and breaks down the door: the two lords, cornered, pretend to have come to put out the fire.

Dom Fuas hides in a trunk to get into the house; he is carried by Semicúpio, who then hides his master Dom Gilvaz in it. While Dom Tibúrcio is courting Sevadilha, Dom Lanserote urges him to choose which of his nieces he will marry. They sit on the trunk. When it is knocked down, the candle goes out: the women arrive on stage for a night scene filled with much confusion. Dom Tibúrcio and Dom Lanserote want to open the trunk, but Dona Nise chases them away by talking about a ghost. Dom Gilvaz thanks Dona Nise, which arouses Dom Fuas’s jealousy. Then Dom Fuas speaks with Dona Clóris, arousing Dom Gilvaz’s jealousy. Semicúpio falls into the trunk. Dom Lanserote and Dom Tibúrcio arrive with light: they open the trunk, out of which comes Semicúpio; as he flees, he blows out the candle and shoves the other characters, who all believe that they are being pushed by their respective companion. The wedding is temporarily cancelled after this quarrel. Dom Gilvaz is waiting for Dona Clóris. He asks Dona Nise to hide him, but Dom Fuas and Dona Clóris find him: they both believe that their lovers have betrayed them. Dom Lanserote has reconciled with his nephew; he summons his nieces and, once again, asks Dom Tibúrcio to choose between them. Dom Fuas, Dom Gilvaz and Semicúpio, dressed as women, accuse Dom Tibúrcio of polygamy: he is forced to leave. In his misfortune, Dom Tibúrcio requires medical care: Dom Fuas, Dom Gilvaz and Semicúpio, dressed as doctors, tell him that he is pregnant; they also prescribe natural remedies to their beloved—marjoram, rosemary and daisy. Dom Gilvaz and his servant break into the garden using a rope. Dom Lanserote is there; he catches Semicúpio and locks him inside the henhouse. By mistake, Dom Fuas sits by the marjoram, and Dom Gilvaz by the rosemary: their lovers come to water the plants and find them: this is the beginning of another fit of jealousy from Dom Fuas and Dona Clóris. Dom Lansarote arrives: the lovers hide in the henhouse, as does Dom Tibúrcio. A judicial officer—Semicúpio in disguise—is with Dom Lanserote: he asks the hiding man to come out of the henhouse and arrests all the lords who walk out of it. In a parodical trial, Semicúpio finds the young women guilty of theft for having stolen the heart of the two lords, and sentences them to marriage; he requests that the costs be covered by Dom Lansarote and Dom Tibúrcio. The weddings put an end to the quarrel between rosemary and marjoram.