Previously one of three families in theorderPrimulales, it underwent considerablegeneric re-alignment oncemolecular phylogenetic methods were used fortaxonomic classification. The order was then submerged in a much enlarged orderEricales and became a greatly enlarged Primulaceaesensu lato (s.l). In this new classification of theAngiosperm Phylogeny Group, each of the Primulales families was reduced to the rank of subfamily of Primulaceaes.l. The original Primulaceae (Primulaceaesensu stricto ors.s.) then became subfamily Primuloideae, and one genus (Maesa) was raised to the rank of a separate subfamily, making four in all.
Botanical drawing ofPrimula officinalis Jacquin. Legend: (A) the whole plant; (2) and (3) vertical cross-sections of the flower; (4) stamen; (5) horizontal cross-section of flower showing the calyx around the flower crown and stigma; (6) the stigma; (7) cross section through the ovary; (8) calyx; (9) seed; (10) cross section of seed[4]
Primulaceae are mostlyherbaceous, having no woody stem, except that someform cushions (spreading mats a few inches high) and their stems are stiffened bylignin. The stems can grow upright (erect) or spread out horizontally and then turn upright (decumbent).[6][7]
Leaves aresimple, being directly attached to the stem by apetiole (stalk), but unlike the leaves of most flowering plants they have nostipules. The petiole is short or the leaf tapers gradually towards the base.Leaf arrangement is typically alternate but some are opposite or whorled, and there is generally a rosette at the base of the stem. The edges are toothed (dentate) or sawtoothed. New leaves in the bud are usuallyinvolute (rolled towards the upper surface) orconduplicate (folded upwards), but a few species roll downwards.[6][7]
Each flower isbisexual, having bothstamens andcarpels. They haveradial symmetry; thepetals can be separate or partially or fullyfused together to form a tube-shapedcorolla that opens up at the mouth to form a bell-like shape (as in item 8 in the figure) or a flat-faced flower. In most of the families of Ericales, stamens alternate with lobes, but in Primulaceae there is a stamen opposite each petal.[8]
Thecalyx has 4 to 9 lobes and persists after flowering.[7] They are grouped in unbranched,indeterminate clusters such as racemes, spikes, corymbs or umbels.[6]
The fruit of Primulaceae begins as anovary and inside it are the future seeds (ovules). These are attached to a central axis without any partitions between them (an arrangement calledfree central placentation; see item 7 in the figure), and they arebitegmic (having a double protective layer around each ovule). Unlike in most other families of Ericales, both layers form the opening at the top (themicropyle).[8]
As seeds develop, anendosperm grows around the embryo through free division of nuclei without forming walls (nuclear endosperm formation). The embryo forms a pair of short, narrowcotyledons (item 10 in the figure). Usually multiple seeds are in acapsule that is carried on a straight stalk (pedicel orscape). After it matures, itsplits apart, releasing the seeds ballistically.[6]
The taxonomic history of Primulaceae has been long and complex. Thebotanical authority for the family name is given toAugust Batsch (1794),[1] as Batschex Borkh, using the term Primulae with six genera, the valid description being subsequently given byBorkhausen (1797).[a][9] Some earlier authors[clarification needed] attributed the name toVentenat (1799), as Primulaceae Vent.,[10] who described the Primulacées,[11] but Batsch had precedence.[2]
Linnaeus (1753) placedPrimula and related primuloid genera in the Hexandria Monogynia (six stamens onepistil) in his sexual classification based on reproductive characteristics.[12]Jussieu arranged Linnaeus' genera in ahierarchical system of ranks based on the relative value of a much wider range of characteristics. In hisGenera plantarum (1789) he organised the primuloid genera into twoOrdo (families), within aclass (VIII) he calledDicotyledones Monopetalae Corolla Hypogyna, based on thecotyledons (two), form of the petals (fused), and position of thecorolla with respect to theovary (below).[13] Jussieu's families were the Lysimachiae, includingPrimula andTheophrasta[14] and theSapotae, includingMyrsine, these being the three main lineages in modern understanding.[15]
The most complete treatment of the Primulaceaefamily, with nearly 1,000species arranged into 22genera, was byPax andKnuth in 1905 in theEngler system. They divided the family into fivetribes (and several subtribes); Androsaceae, Cyclamineae, Lysimachieae, Samoleae and Corideae.[16][17] Many systems since have lacked consistency, but generally recognised two major groups as either tribes or subfamilies, the Lysimachieae and Primuleae (the Androsaceae of Pax and Knuth), with the largest genera beingPrimula,Lysimachia andAndrosace.[18][17]In theCronquist system (1988),Cronquist included the three closely related families, Primulaceae,Myrsinaceae andTheophrastaceae in theorderPrimulales, ofsubclassDilleniidae, based onmorphological characteristics, in particular,ovaries with free-central placentation, a feature consideredsynapomorphic.[19] His circumscription of Primulaceae included about 800 species.[20]
These three families were referred to as the primuloid families.[5] With the later development ofmolecular phylogenetic methods, the Primulales were found to be more closely related to other families within theEricales, and the three primuloid families were subsequently absorbed into an expandedEricales (Ericalessensu lato ors.l.), making 24 families within that order, where the primuloids formed amonophyleticclade.[8] It was also apparent that Myrsinaceae were paraphyletic, unless the genusMaesa wassegregated and elevated to become a newmonogeneric family,Maesaceae, but also that Primulaceae were probably paraphyletic.[21][22][5]
In the first consensus taxonomic classification, theAngiosperm Phylogeny Group (APG 1998), these proposals were recognised by including Primulaceae within Ericales, asEudicots, forming one of three clades in theAsterids (Asteridae).[8][23] Maesa was formally segregated in 2000.[24] Further changes came from analysis of DNA sequence data. This led to the move of genera (primarily terrestrial non-basal-rosette) from Primulaceae to Mysinaceae and Theophrastaceae. At that time Primulaceae was considered to consist of nine tribes (Primuleae, Androsaceae, Ardisiandreae, Lysimachieae, Glauceae, Anagallideae, Corideae, Cyclamineae, and Samoleae).[10] Notably, Lysimachieae and three smaller tribes, Corideae, Cyclamineae and Ardisiandreae, were transferred to Myrsinaceae, and Samoleae to Theophrastaceae. This enlarged Myrsinaceae is distinguished as Myrsinaceaes.l. in comparison to the previous smaller family, Myrsinaceaes.s. (lessMaesa).[17] Some authors[25][26] preferred to raise Samoleae to its own family, Samolaceae, but this has not been accepted by subsequent authors, placing it within Theophrastaceae, while recognising its distinct position within that grouping.[27] These transfers, to preserve monophyly at the family level essentially left two tribes remaining in Primulaceae, the Primuleae and Androsaceae, with about 15 genera sharing a number of common characteristics.[5][19][8] These additional changes were reflected in the 2003 revision of the APG system (APG II), where the now four primuloid families were among 23 in Ericales.[28] This restricted Primulaceaesensu stricto (s.s.) consisted of three groups: The Primulae, includingPrimula, the largest genus; the Androsaceae, includingAndrosace, the second largest genus; together with a small third group containingSoldanella,Hottonia,Omphalogramma andBryocarpum.[18]
The APG third classification system (APG III, 2009) discussed all the taxonomic challenges arising from the phylogenetic studies, and placed all primuloid genera into one large Primulaceaes.l., corresponding to Cronquist's Primulales. They stated that "The biggest problem for APG III was the question of how to treat Primulaceae and their immediate relatives, a closely related group that in the past has often been recognized as a separate order". The decision to treat all genera as a single family was based on the observation that the new circumscriptions had little in the way ofapomorphies, but the entire group had numerous synapomorphies and were easy to recognise. This resulted in an Ericales with 22 families.[27] Consequently, the four primuloid families were reduced to the rank of subfamilies within Primulaceaes.l.[29]
Primulaceaes.l.sensu APG III form part of the speciose (species rich) Asterid order Ericaless.l., with about 12,000 species and 22[b] families as per APG IV. Ericales is one of four major clades within the asterids, where it is sister to theeuasterids.[31] The phylogenetic structure of Ericales, as shown in the followingcladogram, consists of seven major suprafamilial clades (e.g. balsaminoids, styracoids) and a group of "core" Ericales. Within the eracalean families, Primulaceaes.l. is shown as asister group toEbenaceae, and both are sister toSapotaceae. These three families make up the primuloid clade.[30]
Thefossil record of Primulaceaes.l. is sparse, but thecrown group has been estimated as c. 46-61 million years old.[32] The crown primuloids have been dated to c. 102mya, with Primulaceae/Ebenaceae divergence at 80 mya.Crown ages for the Primulaceae subfamilies vary from 24 mya for the Maesoideae, thebasal group, to 70 mya for the Theophrastoideae.[30]
The primuloids probably originated in a sharedNeotropical/Indo-Malaysianancestral range, with the Primulaceae/Ebenaceae clade occupying the neotropics. Theophrastoideae is nearly all neotropical with a more recent migration out of the realm found in the aquaticSamolus genus. The divergence between Theophrastoideae and Primuloideae-Myrsinoideae at 70 mya represents avicariant event between the Neotropics and thePalearctic in the case of the latter. The Primuloideae originating in the Palearctic, persisted till the last 16 mya, when it started to shift into theNearctic.[30]
The three former families of the Primulales, together with the segregated Maesaceae, have beenre-circumscribed into the broadly defined Primulaceaesensu lato (s.l.) The two uniting features of this family are a free central placenta and one stamen opposite each of the corolla lobes.[2][33][27] The cladogram below shows the infrafamilial phylogenetic relationships, together with the subfamilial crown ages. Maesoideae forms the basal group, while Primuloideae andMyrsinoideae are in a sister group relationship.[33][8][29][30]
Christenhusz et al. (2016, 2017) list 53 genera and 2,790 species, varying from 1 in Maesoideae to 38 in Myrsinoideae, with 8 in Theophrastoideae and the remaining 6 in Primuloideae.[34][32] Byng (2014)[29] andPlants of the World Online list 55 accepted genera.[3][33][8][29][30] The generic limits of Myrsinoideae are not fully resolved and the status of a number of genera is under revision.[35]
Maesoideae is amonogeneric subfamily, whose single genus isMaesaForssk. It is a genus of trees. The flowers are small, with short tubules and semi-inferior ovary, arranged in axillary or terminalracemes, or inpanicles.Maesa has about 100 species, and is distributed in both tropical and subtropical regions of the Old World, ranging from East Africa to Japan.[5]
Once included in the Primulaceae tribe Samoleae, it has most commonly been considered as part of family Myrsinaceae, till segregated into its own family[24] and then submerged as a Primulaceaes.l. subfamily. It has characteristics that distinguish it from Myrsinaceae and forms the basal group of the clade as sister to all other subfamilies.[5]
The relatively large Myrsinoideae, has been treated as a number of tribes, e.g. Ardisieae and Myrsineae, and more recently Lysimachiaeae, a transfer from Primulaceaes.s. Ardisieae and Myrsineae represent the woody clades within the subfamily.[30] Within the Myrsinoideae, the genera represented by the restricted Myrsinaceaes.s., prior to the transfers from the then Primulaceae, form a distinct clade.[35] Genera in Lysimachiaeae areTrientalis,Anagallis,Glaux,Lysimachia,Asterolinon andPelletiera.Coris had its own tribe within Primulaceaes.s., Corideae, but its molecular affinities led to its transfer to Myrsinoideae. Similarly,Ardisiandra was the tribe Ardisiandreae andCyclamen the tribe Cyclamineae.[5]
The subfamily is characterised byscaposeinflorescences, distinctly tubular flowers havingcampanulate orhypocrateriform corolla, imbricate corollaaestivation, isodiametric corolla epidermal cells, leaves almost always forming a basal rosette, and ovules rarely immersed in the placenta. In addition they often have syncolpate or sometimes polycolpatepollen, without margo.[5]
Subdivision has included the tribes Androsaceae and Primulae. Takhtajan (1997) gives the four genera of Androsaceae asAndrosace (includingDouglasia),Vitaliana,Stimpsonia andPomatosace, and the ten genera of Primulae asOmphalogramma,Bryocarpum,Primula,Dionysia,Cortusa,Kauffmannia,Hottonia,Srediskya,Dodecatheon andSoldanella.[10]
In contrast Kallersjo et al. (2000) place all genera in Primulae, and list thirteen in all:Androsace,Douglasia,Omphalogramma,Soldanella,Dodecatheon,Cortusa,Primula,Dionysia,Vitaliana,Hottonia,Bryocarpum, andPomatosace. These two (or one) tribes represent the remaining genera in Primuloideae (Primulaceaes.s.) following redistribution among the Primulales on molecular grounds. The 600 species mainly belong toAndrosace andPrimula and belong to the mountainous regions of Europe and Asia (mainly China).[5]
Theophrastoideae consist of a relatively small subfamily, whose flowers arestaminodial and bearberries. The ovary is superior, and the corolla is often tubular. The eight genera are confined to South and Central America.Samolus is a distinct genus, being sister to all other Theophrastoideae. Previously it formed its own tribe, Samoleae within Primulaceaes.s., and in some systems, its own family, Samolaceae, but was subsequently transferred to Theophrastoideae.[5]
^"More additions affectingconserved familial names are from Batsch (1794), which is to be considered as the place for valid publication of Melanthiaceae and Primulaceae, both accepted and conserved with the authorship of'Batsch ex Borkh. 1797' but validly published in 1794 by a reference in the introduction of that book to the corresponding descriptions in Batsch (1786)"[2]
^Ericales has 21 or 22 families, depending on whetherSladeniaceae is recognised as separate from, or submerged inPentaphylacaceae[30]
Tomlinson, P. Barry (2016) [1986]. "Primulaceae (Myrinoideae: Myrsinaceae)".The Botany of Mangroves (2nd ed.). Cambridge University Press. pp. 302–308.ISBN9781316790656.
Angiosperm Phylogeny Group IV; Chase, M. W.; Christenhusz, J. M.; Fay, M. F.; Byng, J. W.; Judd, W. S.; Soltis, D. E.; Mabberley, D. J.; Sennikov, A. N.; Soltis, P. S.; Stevens, P. R. (2016), "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV",Botanical Journal of the Linnean Society,181 (1):1–20,doi:10.1111/boj.12385
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