| Pentapetalae | |
|---|---|
 | |
| Cerasus (Rosaceae) | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| (unranked): | Gunneridae |
| Clade: | Pentapetalae DE Soltis, PS Soltis & WS Judd 2007 |
| Clades and orders[1] | |
| |
Inphylogenetic nomenclature, thePentapetalae are a large group ofeudicots that were informally referred to as the "core eudicots" in some papers onangiospermphylogenetics.[2] They comprise an extremely large and diverse group accounting for about 65% of thespecies richness of theangiosperms, with wide variability inhabit,morphology,chemistry, geographic distribution, and other attributes. Classical systematics, based solely onmorphological information, was not able to recognize this group. In fact, the circumscription of the Pentapetalae as aclade is based on strong evidence obtained from DNA molecular analysis data.[3][4][5]
The Pentapetalae clade is composed of the ordersBerberidopsidales—including the familyAextoxicaceae[6][7]—Caryophyllales,Santalales andSaxifragales, the familiesDilleniaceae andVitaceae and all members of the cladesAsteridae andRosidae.[8]
Phylogenetic analyses of completechloroplast genome sequences have provided a reliable outline of the relationships among the major Pentapetalae lineages and also provide a framework for investigating the evolutionary processes that generated a large proportion of the diversity of extant angiosperms.[9] In light of these phylogenetic results, the current challenge for scientists in this area ofbotany is to identify the characters that are unique to thesuperasterid andsuperrosid clades and those that arose in parallel in both, and then to explore theirevolutionary implications.[10]
Pentapetalae have a characteristic type offlower made up ofwhorls of five pieces, as the name of the clade suggests (fromAncient Greek,penta meaningfive). Theperianth is composed of a differentiatedcalyx andcorolla. The sepals are innervated by three or morevascular bundles corresponding to the vascular system of thepetiole, while thepetals have only one trace. Theandroecium usually has twice as many pieces as the calyx and corona, i.e. is composed of 10stamens, which are arranged in two whorls. When the number of stamens is greater than twice the number of pieces of the perianth, they are arranged in fascicles or in a centrifugal spiral.[2][8]
Pollen grains in the Pentapetalae are characteristically tricolpate. This type of pollen grain has three or more pores within grooves called "colpos". In contrast, most otherspermatophytes—that is,gymnosperms,monocots andpaleodicots—have monoculcate pollen, with a single pore located in a groove called a "sulcus".[2][8]
Thegynoecium of Pentapetalae plants is usually composed of fivecarpels joined together, although gynoeciums formed by three carpels are also quite common. In cases where the gynoecium is composed of only two carpels, they overlap. In general, they present "compitum", a region of thestyle where the stylar canals of the different carpels are united in a single cavity and in which thepollen tubes can change direction of growth from one carpel to another. Theovules are usually ofaxillary placentation. Thepistil, finally, commonly terminates in a style and astigma that is not decurrent. Thefruit is dry and dehiscent, when it is acapsule it showsloculicidal dehiscence. Regarding the interaction betweenpollen and pistil, pentapetalous plants have agametophytic incompatibility system based on theRNAase system.[2][8] Another anatomical characteristic of Pentapetalae is the presence of aclosed root apical meristem. From thephytochemical point of view, this group of plants present cyanogenesis—that is, they biosynthesizecyanogenetic glycosides that by hydrolysis originatecyanide—through themetabolic pathway of branchedamino acids, such asleucine,isoleucine andvaline.[2][8]
Dilleniales are recognized by theirleaves with usually strong and parallel secondaryveins that go straight to the teeth; being common the tertiary scalariform venation. The leaf lamina is usually rough. Also, the leaves tend to elongate when still rolled. Thewood is usually vivid brown. Thepeduncles are jointed near the apex and persist after the flower falls off; the flowers are usually conspicuous, with ruffledpetals and numerousstamens that are reflexed in the bud, usually having porousanthers. Thefruits are smallfollicles containingseeds witharil, thecalyx is persistent, sometimes acrescent, and thefilaments are also persistent.[11]
Berberidopsidales is an order formally accepted only in the most recent phylogenetic classifications of angiosperms,[12][13] comprising two small families,Aextoxicaceae andBerberidopsidaceae, which together include only three genera and four species distributed inChile and easternAustralia. The distinctive characters of the order are largely related to its anatomy, such as the presence of crystals—especiallydrusen—in the leaves and petioles, thevascular bundles of thepetiole form a ring and thestoma of theleaf epidermis are of a particular type called "cyclocytic". Theandroecium hasstamens with rigidfilament and theseeds presentendotesta.
The flowers ofBerberidopsis corallina do not differ insepals andpetals, but exhibit a gradual transition from small outertepals to larger, brightly colored inner tepals. The androcecium consists of a ring of stamens and there are threecarpels with parietalplacentation. In contrast,Aextoxicon has unisexual and pentamerous flowers. Male flowers have a distinctcalyx andcorona and a haplostomous androcecium. Female flowers have the same type of perianth, but the number of pieces is more variable.[14][15]
Given these differences between the two genera belonging to the same family, it has been suggested that the floral development of Berberidopsidales is a "link" in theevolution of the Gunneridae[16][17] flower, and that the floral morphology ofAextoxicon, with features such as the highly variable number of sepals and spirally arranged petals, is also compatible with this hypothesis.[18] However, the position of the Berberidopsidales in the phylogenetic tree is not congruent with it.[19]
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The orderSantalales, with its approximately 160 genera and 2,200 species distributed worldwide, is a monophyletic group that has long occupied an unresolved position at the base of the Gunneridae.[20] Recently, phylogenetic studies based on molecular data from the complete chloroplast genome indicate a position of Santalales at the base of the Asterids.[21] Santalales is ecologically diverse and includes free-living plants, such asErythropalum, as well as (hemi)parasites. Among the latter are species that parasitizestems or shoots, such as the mistletoes of the genusMisodendrum, androot parasites, including the well-known and economically important sandalwood tree (Santalum album), whose aromatic wood is a component of many perfumes.[22][23][24] TheAPG III classification system recognized seven families in Santalales:Balanophoraceae,Misodendraceae,Opiliaceae,Schoepfiaceae,Loranthaceae,Santalaceae (includingViscaceae), andOlacaceae.[1] In 2010, however, new molecular data have made it possible to revise that conclusion, so thatAptandraceae,Balanophoraceae,Coulaceae,Erythropalaceae,Loranthaceae,Misodendraceae,Octonemaceae,Olacaceae,Opiliaceae,Santalaceae,Schoepfiaceae,Strombosiaceae, andXimeniaceae are now recognized.[25]
Therosids are a large group ofeudicotyledons containing approximately 70 000 species,[26] more than a quarter of the total number of angiosperm species.[27] It has been subdivided into some 16 to 20 orders, depending on the circumscription and classification adopted. These orders, in turn, comprise about 140families.[28] Together with the asterids, they constitute the two largest groups of eudicotyledons.
The rosids share a few morphological characteristics that distinguish them from other groups, such as the presence ofnectaries in the floral receptacle, the long embryo and the distinctive mucilaginous cells. At the molecular level, the rosids are characterized by the loss of function of thechloroplastinfAgene and the absence of thecoxII.i3intron in themitochondrion.[2]
Theasterids are a large group ofeudicotyledons that includes approximately 80 000 species, grouped in 13 orders and more than a hundredfamilies,[26] and between a third and a quarter of the total number ofangiosperm species.[27][28] Together with therosids, they constitute the two largest groups of eudicotyledons. They represent the mostapotypic clade of the angiosperms, or, as it is inappropriately called, "most evolved". The group most likely originated in theCenozoic, about 50 million years ago, and its success is related to its adaptation toinsect pollinators. Four of the largest families of angiosperms belong to thisclade: theAsteraceae, theRubiaceae, theLamiaceae and theApocynaceae.[2]
The plants belonging to this clade are characterized by being herbaceous, withhermaphrodite,zygomorphicflowers—that is, they admit only one plane of symmetry—that are pollinated by insects. In addition, thestamens are arranged in a circle and thepetals of thecorona are joined together forming a tube. Thegynoecium is formed by two weldedcarpels. The flowers are often arranged in tightinflorescences, such as theears of thelabiatae andplantaginaceae or thecapitula (heads) of thecompositae.[2]
The age of this clade has been estimated at 113 to 116 million years.[29][30][19] The oldestmacrofossils of eudicots, which unfortunately cannot be attributed to any extant group, belong to theCretaceous-Cenomanian, just 96–94 million years old.[19]
Analyses of complete chloroplast genome sequences allowed us to resolve the relationships among the major Pentapetalae clades. Immediately after diverging from theGunnerales, the Pentapetalae diverged into three major subclades: (i) the Dileniaceae, (ii) the superrosid clade including theSaxifragales,Vitaceae andRosids, and (iii) the superasterid clade composed of theBerberidopsidales,Santalales,Caryophyllales andAsterids. The close relationship demonstrated at the molecular scale between Saxifragales, Vitaceae and rosids is congruent with their morphological affinities. In fact, these clades form the so-called "core of the rosids" in theCronquist andTakhtajan classification systems.[31][32] They all have anandrocecium with jointedanthers, leaves withstipules, theendosperm withnuclear formation, and amicropyle that forms from the outer integument or both integuments.[33][34][19]
Several putativesynapomorphies may also characterize the superasterid clade. Thus, the "psyllulate" pollen or with a granular structure of theexine, the presence ofsclereids in the leaves, the isomerism of the androcecium and the fused carpels unite the santalales, the caryophyllales and the asterids. Likewise, leaves without stipules may be another synapomorphic character, althoughBerberidopsidaceae have stipules andAextoxicaceae lack them; thus, the ancestral status of Berberidopsidales and asterids is still unclear.[2][19]
The initial divergence between the Dilleniales, superrosids and superasterids must have occurred very quickly, within a period of one million years after the initial separation of the Pentapetalae from the Gunnerales. Likewise, the superrosids and superasterids show an early and very rapid divergence since the lineages that led to the Vitaceae, Saxifragales, and rosids arose within a period of only five million years, as did those that led to the appearance of the Berberidopsidales, Caryophyllales, and asterids.[19]
The followingcladogram summarizes the phylogenetic relationships within the Pentapetalae clade and this clade.[35][36]
| eudicots |
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The names lamiids (for euasterids I) and campanulids (for euasterids II) were suggested by Bremeret al. (2002) and later suggested fabiids (for eurosids I) and malvids (for eurosids II).