''Literature/BlackTrillium'' is a 1990 {{fantasy}} novel [[RoundRobin co-written]] by AndreNorton, MarionZimmerBradley, and Julian May. It is also the first book in the ''Trillium'' series, consisting of four more novels set in the same universe and featuring more or less the same cast. After the original novel, however, the three co-authors decided to write the sequels separately, so there are effectively [[AlternateTimeline three mutually exclusive continuities]], of which ''Black Trillium'' is the lowest (and only) denominator.

* '''''Black Trillium''''' (1990). The original novel begins with the [[TheEmpire evil kingdom of Labornok]] conquering the [[TheFederation neighboring kingdom of Ruwenda]]. The only remnant of the Ruwendan [[RoyalBlood royal family]] are the [[EverythingsBetterWithPrincesses young triplet princesses]], who are rescued by their servants and smuggled across the conquered country to [[TheObiWan the White Lady]], who was supposed to protect Ruwenda from the invasion. From there on, the three princesses must brave three different paths to retrieve [[RuleOfThree three parts]] of the mightiest weapon left behind by ThePrecursors, the [[DismantledMacGuffin Scepter of Power]].
* '''''Blood Trillium''''' (1992, May).
* '''''Golden Trillium''''' (1993, Norton). Some time after the conclusion of ''BT'', [[LadyOfWar Kadiya, the second princess]], leads an expedition into the [[SwampsAreEvil Thorny Hell]] to uncover a few of the Ancient's secrets.
* '''''Lady of the Trillium''''' (1995, Zimmer Bradley). [[TimeSkip 900 years after]] the ''BT'', [[BadassBookworm Haramis, the oldest princess]] and the current White Lady, is faced with the challenge of selecting and educating a successor for herself.
* '''''Sky Trillium''''' (1997, May).

The principle characters of the novels are:

* Haramis, the oldest of the three princesses. [[TheSpock A bookworm since childhood]], she is the most intelligent of the three and her mastery of magic soon surpasses pretty much everyone in the world. Her personal artifact is the Three Winged Circle (a wand) and since the end of ''BT'', she is known as the White Lady and the Arch-Sorceress of the Land. In the original novel, her chapters were written by Marion Zimmer Bradley.
* Kadiya, the second princess, is a LadyOfWar and has a [[TheMcCoy brash, passionate personality]], often putting her at odds with the logical Haramis (especially in May's continuity). Her personal artifact is the Three Lobed Burning Eye (a sword) and after ''BT'', she is known as the Lady of the Sacred Eyes, serving as the protector of the Oddlings. In the original novel, her chapters were written by Andre Norton.
* Anigel, the youngest princess. A PrincessClassic who [[TheKirk mediates the other two]] and seeks diplomatic solutions. Her personal artifact is the Three Headed Monster (a crown) and after ''BT'', she succeeds her father as a queen of Ruwenda, immediately marrying Antar, the prince of Labornok, and uniting the two kingdoms into Laboruwenda. In the original novel, her chapters were written by Julian May.
* Orogastus, alias Portolanus. The EvilSorcerer who was [[TheManBehindTheMan really behind Labornok's aggression]] and an [[DatingCatwoman on-and-off love interest for Haramis]]. His role and motivation are greatly expanded in May's continuity.
* Antar, the Crown Prince of Labornok. TheWisePrince who mistrusts Orogastus and later defects to Anigel's army and eventually marries her. In May's continuity he often plays the DistressedDamsel role for Anigel.
----
!!The novel and the subsequent series contain examples of following tropes:

* AlternateTimeline: The original novel is the only one whose plot canonically happens in all three continuities, although Norton and Zimmer Bradley's continuities don't contradict each other (since they only concern their respective heroine and are chronologically 900 years apart).
* BadassBookworm: Haramis, after learning magic.
* DamselInDistress: Surprisingly, it is Antar who often causes trouble to his frail princess wife Anigel.
* DatingCatwoman: Haramis and Orogastus have... an uneasy relationship. [[spoiler:Although in the end of ''Sky Trillium'', they seem to finally get together, after Orogastus settles down as the Arch-Wizard of the Sky.]]
* DismantledMacGuffin: The Scepter of Power.
* TheEmpire: Labornok is a militaristic, expansionist human kingdom.
* EverythingsBetterWithPrincesses
* EvilSorcerer: Orogastus, who becomes an AntiVillain in May's continuity.
* TheFederation: Ruwenda is an aging kingdom that unites both humans and oddlings, and the only reason why it wasn't conquered for so long was White Lady's protection.
* LadyOfWar: Kadiya is the warrior princess.
* TheManBehindTheMan: Orogastus manipulated the King of Labornok to declare war.
* MeaningfulName: Anigel is just one letter removed from "angel".
* TheObiWan: White Lady Binah.
* PowerTrio: The three princesses. Let's see...
** BeautyBrainsAndBrawn: Anigel, Haramis, and Kadiya, respectively.
** BlondeBrunetteRedhead: Ditto.
** FreudianTrio: Haramis = TheSpock, Kadiya = TheMcCoy, Anigel = TheKirk.
* PrincessClassic: Anigel.
* RoundRobin: How the original novel was written.
* RoyalBlood: All main characters except Orogastus are royals.
* RuleOfThree: The series ''runneth over'' with it, especially May's continuity.
* SwampsAreEvil: The Thorny Hell is probably the single nastiest place on the planet.
* TimeSkip: ''Lady of the Trillium'' fast forwards the narration 900 years into the future, when Haramis realizes that she will soon die of old age.
* TheWisePrince: Antar, whose HeelFaceTurn was foreseeable from the moment his was introduced.
----