Rosales
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1. Supertaxonomy Overview
The Rosales are a major order of Rosid flowering plants containing roses, apples, pears, cherries, peaches, plums, strawberries, raspberries, blackberries, almonds, figs, mulberries, breadfruit, jackfruit, elms, nettles, hemp, hops, hackberries, jujubes, buckthorns, sea buckthorn, silverberries, and thousands of other trees, shrubs, vines, and herbs. Within the Tree TSAR framework, Rosales belong to the Rosids and are one of the four orders constituting the newly restricted Fabids under APG V. The order contains nine living families: Rosaceae, Rhamnaceae, Elaeagnaceae, Barbeyaceae, Dirachmaceae, Ulmaceae, Cannabaceae, Moraceae, and Urticaceae. Together they comprise roughly 8,000 living species in close to 300 accepted generic entities, making Rosales one of the larger and most economically important radiations within the Rosids.
Rosales are also one of the clearest examples of how molecular systematics overturned a familiar morphology-based order concept. Traditional Rosales centered on the Rose Family and other plants thought to resemble it in flower or fruit, whereas elms, figs, nettles, hemp, hops, and their relatives were usually placed in Urticales. Buckthorns and allied families were likewise classified elsewhere. Molecular evidence revealed that these apparently different assemblages belong to the same evolutionary lineage. The modern order therefore contains both the conspicuous, often showy flowers and extraordinary fruit diversity of Rosaceae and the much more reduced floral systems of the old urticalean complex.
This contrast gives Rosales an unusually broad biological identity. Some members are insect-pollinated shrubs and fruit trees with large flowers; others bear minute greenish flowers adapted to wind pollination. Fruits include drupes, pomes, achenes, follicles, aggregate fruits, samaras, drupaceous structures, and highly specialized multiple fruits. The order ranges from herbaceous nettles and strawberries to giant tropical figs and long-lived temperate elms. No single visible feature defines the whole lineage, and its modern unity is primarily phylogenetic.
Rosales are also a major component of the broader nitrogen-fixing radiation. Actinorhizal symbioses with Frankia occur in Elaeagnaceae, portions of Rhamnaceae, and Dryadoideae within Rosaceae. Even more unusual is the Trema lineage historically recognized as Parasponia, which contains the only known non-legume plants capable of forming conventional rhizobial root nodules. These symbioses do not characterize Rosales as a whole, but they make the order especially important for understanding the evolutionary assembly of root-nodule nitrogen fixation across the Fabids.
2. Placement in Tree TSAR
Within Tree TSAR, Rosales occupy the pathway Seed Plants → Angiosperms → Core Eudicots → Superrosids → Rosids → Rosales. APG V places Rosales within the Fabids together with Fabales, Fagales, and Cucurbitales, but Tree TSAR does not require Fabids as an additional fixed ribbon level. As on the Fabales page, the Fabid concept remains biologically important and is discussed throughout the narrative, especially in relation to nitrogen-fixing symbioses, while the stable navigational pathway moves directly from Rosids to Rosales.
Rosaceae therefore follow Rosaceae → Rosales → Rosids → Superrosids → Core Eudicots → Angiosperms → Seed Plants. The same route applies to Rhamnaceae, Elaeagnaceae, Barbeyaceae, Dirachmaceae, Ulmaceae, Cannabaceae, Moraceae, and Urticaceae. The result is a strikingly unified pathway for plants that older systems placed far apart. A rose, fig, elm, nettle, cannabis plant, and sea buckthorn all converge at the same ordinal node before joining the larger Rosid radiation.
APG V retains the nine-family circumscription of Rosales, so the order itself is exceptionally secure. Most current uncertainty lies in the branching sequence among several ancient families, particularly on the Rhamnaceae-Elaeagnaceae side of the tree. This makes Rosales an ideal example of the Tree TSAR principle that a stable clade does not require every internal node to be equally well resolved.
3. Evolutionary History and Fossil Context
Rosales originated during the Cretaceous diversification of the Rosids, with molecular estimates generally placing the crown near the Early-Late Cretaceous transition or somewhat earlier. The order’s early history appears to have involved rapid splitting among several family lineages. A major 2011 multi-gene analysis strongly supported Rosaceae as sister to the remainder and recovered two broad branches among the remaining families: a rhamnalean assemblage containing Rhamnaceae, Elaeagnaceae, Barbeyaceae, and Dirachmaceae, and an urticalean assemblage containing Ulmaceae, Cannabaceae, Moraceae, and Urticaceae (Zhang et al. 2011). That framework remains useful, but modern genomic data show that the deeper history was more reticulate and less neatly bifurcating than the older tree suggested.
A major phylogenomic study published in 2026 compared nuclear, plastid, and mitochondrial histories across all nine families and documented extensive conflict among genomic compartments. Liu et al. (2026) identified incomplete lineage sorting as a major contributor to unstable family positions and found evidence that ancient hybridization affected the histories of Rhamnaceae and Elaeagnaceae. Rosales therefore provide a particularly strong example of rapid ancient radiation leaving persistent genomic signatures. The family tree is real and recoverable, but different genomes need not preserve every early event in exactly the same way.
The fossil record confirms the antiquity of several principal branches. Rosaceae possess Late Cretaceous floral fossils and are commonly inferred from molecular data to have originated around 100 million years ago or somewhat earlier. By the Paleocene and Eocene, recognizable lineages related to Prunus, , , and other modern groups were established. The urticalean side also extends deep into the Cretaceous. Pollen with ulmoid and celtoid features occurs by roughly the Turonian, followed by more distinctive hackberry- and elm-like fossils later in the Late Cretaceous. These records demonstrate that the lineages leading to elms, hackberries, figs, nettles, and their relatives had already acquired substantial morphological differentiation before the end-Cretaceous mass extinction (Sytsma et al. 2002).
Moraceae and Rhamnaceae also possess deep fossil histories, although the confidence of individual records varies. By the Paleogene, the order had become a major component of Northern Hemisphere forests as well as tropical and subtropical vegetation. Warm Eocene climates allowed several lineages to occupy regions much farther poleward than their modern distributions suggest, after which cooling, aridification, mountain building, extinction, and dispersal reshaped their ranges. Rosales therefore combine an ancient Cretaceous origin with repeated later radiations in temperate forests, tropical forests, open drylands, and agricultural landscapes.
These fossils illuminate evolutionary age, former geography, and ecological expansion without automatically assigning every extinct form to a living family. The order’s history is best understood as more than 100 million years of branching, extinction, genome evolution, hybridization, symbiosis, and ecological change rather than as a simple linear progression toward modern forms.
4. Classification and Circumscription
The name Rosales Bercht. & J.Presl dates to 1820, but modern Rosales are very different from many historical versions of the order. Earlier systems often used Rosales for plants considered morphologically rose-like, while the reduced-flowered elm-nettle-fig assemblage was placed in Urticales. Rhamnaceae and its allies were often assigned to Rhamnales or distributed elsewhere. Molecular phylogenetics demonstrated that these divisions did not correspond to the deeper evolutionary tree and gradually produced the modern nine-family circumscription.
The collapse of Urticales into Rosales brought several important family-level changes. Traditional Celtidaceae, centered on hackberries and relatives, could not be maintained once molecular analyses showed that Cannabis and Humulus were nested within the broader hackberry lineage. Modern Cannabaceae therefore include hemp, hops, Celtis, Trema, Aphananthe, Gironniera, Pteroceltis, and related genera. Cecropiaceae likewise proved to be nested within Urticaceae, so Cecropia and allied genera are now part of the nettle family despite their very different growth form and ecology. Modern Ulmaceae consequently became much narrower and now center on Ulmus, Zelkova, Planera, and several mostly tropical genera rather than on the old elm-hackberry assemblage.
The rhamnalean side contains its own classificatory surprises. Barbeyaceae consist only of Barbeya oleoides, while Dirachmaceae comprise the genus Dirachma, with two accepted species. Both were difficult to place morphologically and were associated with several different families before molecular evidence securely embedded them within Rosales. Elaeagnaceae, Rhamnaceae, Barbeyaceae, and Dirachmaceae form a recognizable broad portion of the order, but the exact sequence of their divergences has changed among analyses. Older combined-gene work strongly supported a ladder-like arrangement in which Rhamnaceae diverged before Elaeagnaceae and then Barbeyaceae + Dirachmaceae; newer genomic evidence shows that the history is more complicated and influenced by incomplete lineage sorting and ancient hybridization.
The urticalean branch has generally been easier to recognize, with Ulmaceae, Cannabaceae, Moraceae, and Urticaceae forming a strong natural grouping. Even here, however, family relationships and generic limits have evolved as sampling improved. The classification is best presented at the level where confidence is high: Rosales are monophyletic, nine living families are securely recognized, major internal assemblages are real, and some of the earliest family splits remain genomically complex. APG V appropriately retains the order without forcing a more brittle family ladder than the evidence warrants.
5. Morphology, Biology, and Identification
Rosales possess no universal field character, but several recurring themes connect portions of the order. Stipules are frequent, although they may be conspicuous, minute, caducous, transformed into spines, or absent. Leaves are usually alternate, with numerous exceptions. Flowers in the more conspicuously petaliferous families often retain a five-parted rosid pattern, and a hypanthium or floral cup is common in Rosaceae and several allied groups. On the urticalean side, however, the perianth may be strongly reduced, petals can be absent, and unisexual flowers are common. The morphological range is therefore broad enough that identification normally proceeds through family-level character combinations rather than a single ordinal key.
Rosaceae display the most familiar floral architecture. Many species have five sepals, five petals, numerous stamens, and one to many carpels borne on or within a hypanthium, but the family is even more famous for fruit diversity. Prunus produces drupes; apples and pears produce pomes involving substantial accessory tissue; strawberries develop an enlarged receptacle carrying numerous achenes; raspberries and blackberries bear aggregate drupelets; roses form hips surrounding multiple achenes; and spireas and allies commonly produce follicles. Phylogenomic studies demonstrate that fleshy fruits evolved repeatedly within the family rather than from a single fleshy-fruited ancestor (Xiang et al. 2017).
The urticalean families show a very different syndrome. Flowers are often small, greenish, apetalous, and unisexual, with wind pollination widespread. In many Urticaceae and Moraceae the stamens are inflexed in bud and spring outward at anthesis, ejecting pollen. Moraceae frequently possess milky latex and highly condensed inflorescences, reaching an extreme in the Ficus syconium: the apparent “fig fruit” is actually a hollow inflorescence containing numerous tiny flowers. Urticaceae often contain cystoliths and specialized hairs; some genera bear stinging hairs, although stinging is not a family-wide trait. Cannabaceae commonly have simple serrate leaves with strong basal veins, while hemp departs from this pattern through its palmately compound leaves. Ulmaceae often have simple, alternate, serrate leaves with asymmetrical bases, and elm fruits are characteristically winged samaras.
Rhamnaceae and Elaeagnaceae add still other recognizable patterns. Rhamnaceae commonly have small flowers with a conspicuous nectar disk and stamens positioned opposite the petals; spinescent shoots and adaptation to dry climates are frequent. Elaeagnaceae are often distinctive vegetatively because silvery or rusty peltate scales cover the leaves, young shoots, or fruits, and their flowers typically lack ordinary petals. The order’s most biologically unusual feature is its patchy distribution of root-nodule symbiosis. Frankia nodulation occurs in Elaeagnaceae, several Rhamnaceae, and Dryadoideae within Rosaceae, while the Trema lineage historically called Parasponia nodulates with rhizobia. Most Rosales do not fix nitrogen, but these lineages make the order exceptionally important for understanding how nodulation evolved within the Fabids.
6. Distribution and Ecology
Rosales occur essentially worldwide and occupy tropical rainforest, temperate forest, Mediterranean woodland, savanna, grassland, alpine vegetation, dry shrubland, riverbanks, coastal habitats, disturbed ground, and agricultural landscapes. Rosaceae are especially prominent in temperate and subtropical regions of the Northern Hemisphere, where roses, cherries, apples, hawthorns, serviceberries, mountain-ashes, raspberries, and numerous other lineages contribute to forests, shrublands, meadows, and montane communities. Some members reach ecological extremes: Polylepis forms woodlands at extraordinary elevations in the Andes, while dryland Rosaceae such as Cercocarpus and Purshia occupy open western North American landscapes.
The old urticalean families are more strongly tropical overall. Moraceae are major elements of tropical and subtropical forests, and figs represent one of the great woody radiations of the tropics. Urticaceae are especially diverse in humid forest understories, cloud forests, disturbed habitats, and pioneer vegetation, with Pilea, Elatostema, Cecropia, and related genera occupying ecological roles very different from temperate stinging nettles. Cannabaceae range from tropical hackberries and Trema to temperate hemp and hops, while Ulmaceae contribute both Northern Hemisphere forest trees and tropical genera.
Rhamnaceae and Elaeagnaceae contain many species adapted to open, dry, disturbed, or nutrient-poor habitats. Rhamnaceae are diverse in Mediterranean, warm-temperate, subtropical, and dry tropical vegetation, while Elaeagnaceae include shrubs and small trees capable of colonizing poor soils because of their Frankia symbioses. Native Ceanothus, Hippophae, Shepherdia, and Elaeagnus can influence succession and nutrient cycling through nitrogen input. The same traits, however, can contribute to invasiveness when some species are introduced outside their natural ranges; several buckthorns and Elaeagnus species alter understory structure, riparian vegetation, and soil nutrient dynamics in invaded ecosystems.
Rosales also include some of the best-known plant-animal mutualisms. The relationship between Ficus and fig wasps is a classic example of obligate pollination mutualism: female wasps enter receptive syconia, pollinate internal flowers, and reproduce within a subset of them. Figs then support extensive vertebrate food webs because different species fruit asynchronously and can provide resources when other fruits are scarce. Rosaceae contribute equally important flowers and fruits for insects, birds, and mammals, while elms use wind both for pollination and dispersal. The order’s ecology therefore spans highly specialized mutualisms, generalized animal dispersal, wind pollination, wind dispersal, and microbial nitrogen-fixing symbioses.
7. Human Uses and Cultural Importance
Rosales are among the most economically important flowering-plant orders, especially through Rosaceae. Apples, pears, peaches, nectarines, plums, cherries, apricots, almonds, strawberries, raspberries, blackberries, quinces, loquats, and numerous regional fruits all belong to the family. Modern horticulture has generated thousands of cultivars, rootstocks, clonal selections, and interspecific hybrids from these lineages. Moraceae add cultivated figs, mulberries, breadfruit, jackfruit, and other tropical foods, while Rhamnaceae provide jujubes and Elaeagnaceae supply sea buckthorn, buffaloberries, goumi, and related fruits.
Cannabaceae contribute two plants of extraordinary cultural significance. Humulus lupulus provides hops, whose bitter resins and aromatic compounds are fundamental to beer production. Cannabis sativa has been cultivated for millennia for fiber, seed, oil, medicinal compounds, and psychoactive products, while industrial hemp historically supplied rope, sailcloth, textiles, and paper. Urticaceae contain additional fiber plants, most notably ramie (Boehmeria nivea), and nettles have long been used for fiber, food, medicine, and dye. Mulberry cultivation created another global historical connection because Morus leaves feed domesticated silkworms; Moraceae therefore became inseparable from the development of silk production and Eurasian trade.
Rosales also dominate large sectors of ornamental horticulture. Roses alone have generated centuries of breeding and enormous cultivar diversity, while flowering cherries, crabapples, hawthorns, spireas, cotoneasters, pyracanthas, ninebarks, serviceberries, mountain-ashes, and potentillas are staples of temperate landscapes. Elms and zelkovas have long been important street and shade trees, and modern disease-resistant elm breeding continues to shape urban forestry. Rhamnaceae and Elaeagnaceae contribute ornamentals and restoration plants adapted to dry or difficult sites.
The cultural importance of the order extends well beyond utility. Roses carry symbolism associated with love, beauty, secrecy, religion, heraldry, and politics. Apples and figs occupy central places in mythology, religion, folklore, and regional cuisines. Cannabis has accumulated medicinal, spiritual, industrial, recreational, legal, and political meanings across cultures, while hops became deeply embedded in European brewing traditions. Rosales therefore connect modern phylogenetic classification with orchards, gardens, forests, textiles, brewing, silk production, restoration, and some of the most culturally recognizable plants in human history.
8. Conservation Significance
Rosales combine globally abundant crops with serious conservation challenges. One of the clearest examples is the history of Dutch elm disease, which transformed natural and urban elm populations across Europe and North America during the twentieth century. The disease removed enormous numbers of mature trees and changed the character of streetscapes and forests, yet native elm populations persisted through juveniles, sprouts, resistant individuals, and surviving regional gene pools. Contemporary elm conservation therefore requires long-term disease-resistance breeding, preservation of native genetic diversity, restoration, pathogen research, and careful deployment of resistant selections rather than a simple replacement strategy.
Tropical Moraceae and Urticaceae face very different pressures. Deforestation, fragmentation, mining, altered disturbance regimes, invasive species, and climate change threaten large numbers of tropical trees, shrubs, and herbs. Figs deserve special attention because their ecological importance extends well beyond individual species: loss of fig diversity can reduce food availability for birds, bats, primates, and other animals while disrupting specialized fig-wasp pollination systems. Many tropical Moraceae are also important timber or food trees, tying conservation directly to local livelihoods.
Crop-wild-relative conservation is especially important in Rosaceae. Wild apples, pears, cherries, peaches, plums, almonds, strawberries, raspberries, and blackberries preserve genetic variation for pathogen resistance, drought tolerance, heat response, cold hardiness, and other traits critical to future breeding. Because many commercial cultivars are clonally propagated, the genetic diversity represented in orchards can be extremely narrow compared with that retained in wild populations. Prunus africana provides another instructive case: its bark is harvested internationally for medicinal products, and sustainable management must balance commercial demand with regeneration and montane forest conservation.
The species-poor families represent a different kind of conservation value. Barbeyaceae consist of a single living species, Barbeya oleoides, while Dirachmaceae contain only two accepted species of Dirachma. Even where global threat status is not extreme, each surviving population represents a substantial fraction of the evolutionary history of its family. Dirachma socotrana is especially important because of its narrow Socotran range and vulnerability to browsing, habitat degradation, and poor regeneration. Conservation across Rosales must also distinguish between protecting native diversity and controlling invasive members: Rhamnus cathartica, Frangula alnus, Elaeagnus angustifolia, E. umbellata, and other introduced species can alter forests and open habitats outside their native ranges.
9. Major Included Groups
Rosaceae
Rosaceae, the Rose Family, form one of the largest and most economically important families of Rosales, with roughly 3,000 species and close to 100 accepted generic entities. The present treatment recognizes the three major modern subfamilies Amygdaloideae, Dryadoideae, and Rosoideae. Amygdaloideae contain many of the principal woody fruit crops, including Prunus, Malus, Pyrus, and their relatives, together with Spiraea, Crataegus, Amelanchier, Cotoneaster, and numerous other woody groups. Rosoideae include Rosa, Rubus, Fragaria, Potentilla, Alchemilla, and many herbaceous and shrubby lineages. Dryadoideae are smaller but particularly important in the evolution of actinorhizal nitrogen fixation through genera such as Dryas, Cercocarpus, Purshia, and Chamaebatia. The family is also notable for repeated shifts in fruit architecture, hybridization, polyploidy, apomixis in several groups, and substantial horticultural selection.
Rhamnaceae
Rhamnaceae, the buckthorn family, contain roughly 60-65 accepted genera and around a thousand living species. The family includes buckthorns, jujubes, Ceanothus, Colletia, Discaria, Pomaderris, Gouania, and numerous tropical trees, shrubs, and climbers. Flowers are usually small, often with a conspicuous nectar disk, and the stamens characteristically stand opposite the petals. Many species are spinescent or adapted to dry and seasonally dry environments. Several lineages form actinorhizal nodules with Frankia, including the North American Ceanothus radiation. Rhamnaceae are also central to the remaining phylogenetic complexity of Rosales because their position relative to Elaeagnaceae and the Barbeyaceae-Dirachmaceae lineages is affected by ancient incomplete lineage sorting and reticulation.
Elaeagnaceae
Elaeagnaceae, the oleaster family, contain only three accepted genera: Elaeagnus, Hippophae, and Shepherdia. They are shrubs or small trees of temperate and subtropical regions, especially across Eurasia and North America, and are often immediately recognizable by silvery or rusty scales covering leaves, shoots, or fruits. The flowers generally lack ordinary petals, with sepals assuming the primary perianth function. The family is especially important biologically because Frankia root nodules allow many members to colonize nutrient-poor or disturbed substrates. Hippophae rhamnoides is cultivated for its orange fruits and oils, while buffaloberries, goumi, and other species have food or horticultural value. Several Elaeagnus species have also become invasive where introduced outside their native ranges.
Barbeyaceae
Barbeyaceae are one of the smallest living flowering-plant families, containing only Barbeya oleoides. The species is native to northeastern Africa and the southwestern Arabian Peninsula and grows as a shrub or tree in dry woodland and shrubland. Its morphology historically prompted comparison with Ulmaceae and Urticaceae, but molecular evidence places it securely within the rhamnalean portion of Rosales. Older analyses strongly paired Barbeyaceae with Dirachmaceae, whereas newer genomic work shows that the relationships among these small families, Elaeagnaceae, and Rhamnaceae should be interpreted in light of rapid ancient radiation and incomplete lineage sorting. The family’s single-species status makes Barbeya disproportionately important as a surviving branch of Rosalean evolutionary history.
Dirachmaceae
Dirachmaceae consist of Dirachma, with two accepted species, D. socotrana and D. somalensis. The genus is restricted to Socotra and Somalia and therefore represents one of the most geographically constrained lineages in the order. Dirachma socotrana was for many years the only known species of the family, and its combination of stipules, glandular hairs, floral disks, and gynoecial characters contributed to several historical placement hypotheses. Molecular data now secure Dirachmaceae within Rosales, while conservation concern remains high because of the family’s tiny species count and narrow range. Protecting even a few populations can preserve a remarkably deep branch of flowering-plant history.
Ulmaceae
Ulmaceae, the elm family, are much narrower today than in traditional classifications. Modern treatments include Ulmus, Zelkova, Planera, Ampelocera, Hemiptelea, Holoptelea, and Phyllostylon, while hackberries and their relatives have moved to Cannabaceae. Elms are major temperate forest, riparian, street, and shade trees, and their flattened samaras are among the most recognizable fruits in the order. Zelkovas include important relict species with disjunct distributions across western Eurasia and eastern Asia. Dutch elm disease profoundly altered the ecology and cultural history of the family, making Ulmaceae a major case study in disease resistance, conservation breeding, and restoration of long-lived trees.
Cannabaceae
Cannabaceae, the hemp or hackberry family, contain roughly ten accepted genera and more than a hundred living species. Modern circumscription unites Cannabis and Humulus with Celtis, Trema, Aphananthe, Gironniera, Pteroceltis, and several smaller genera. This arrangement differs dramatically from older systems that placed hackberries in Ulmaceae or Celtidaceae. One of the most biologically important members is the Trema lineage historically recognized as Parasponia, whose species form rhizobial root nodules despite not being legumes. Much of the nitrogen-fixation literature continues to use Parasponia, whereas current Kew taxonomy places those plants within Trema; Biological usage of Parasponia must therefore be distinguished from the accepted generic circumscription.
Moraceae
Moraceae, the mulberry or fig family, contain roughly 1,000-1,300 species in about 45-50 genera, including Ficus, Artocarpus, Morus, Maclura, Brosimum, Dorstenia, Broussonetia, and Castilla. The family is predominantly tropical and woody, and milky latex is widespread. Dense, specialized inflorescences occur repeatedly, reaching their most remarkable form in Ficus, where the syconium encloses numerous tiny flowers inside a hollow receptacle. The obligate pollination relationship between figs and fig wasps is one of the classic mutualisms in evolutionary biology. Moraceae also contain major food plants such as figs, mulberries, breadfruit, and jackfruit, as well as numerous ecologically important forest trees.
Urticaceae
Urticaceae, the nettle family, are one of the largest Rosales families, with well over 2,000 species in roughly 60 genera. They include Urtica, Pilea, Elatostema, Boehmeria, Dendrocnide, Cecropia, Coussapoa, Laportea, and Parietaria. Herbs are common, but the family also contains shrubs, trees, epiphytes, and climbing or hemiepiphytic forms. Stinging hairs characterize famous genera such as Urtica and Dendrocnide but are not universal. One of the most consequential modern changes in circumscription was the incorporation of Cecropiaceae, placing Cecropia and related tropical pioneer trees within Urticaceae. The family also has human importance through ramie and other fiber plants, edible nettles, medicinal species, and ecologically dominant tropical pioneers.
10. Similar, Overlapping, or Historically Confused Groups
Rosales and Rosaceae are not synonymous. Rosaceae are one of nine families within the order. A rose, apple, or cherry belongs to both Rosaceae and Rosales, whereas a fig, elm, nettle, hemp plant, or buckthorn belongs to Rosales but not Rosaceae. The common phrase “rose order” is therefore acceptable only if it is not taken to imply that most members look like roses.
The most important historical overlap is Urticales, which traditionally contained elms, hackberries, hemp, hops, figs, mulberries, nettles, and related groups. Molecular evidence showed that this radiation is nested within Rosales, so Urticales is no longer recognized as a separate APG order. The informal term urticalean rosids remains useful for Ulmaceae, Cannabaceae, Moraceae, and Urticaceae. Rhamnales is another historical order now absorbed into modern Rosales through the placement of Rhamnaceae and allied families.
Several family names survive in older literature but no longer represent accepted modern circumscriptions. Celtidaceae has been absorbed into expanded Cannabaceae because the traditional hackberry family would otherwise be paraphyletic relative to hemp and hops. Cecropiaceae has been absorbed into Urticaceae because Cecropia and its allies are nested within the nettle family. The Parasponia problem is a lower-level example: many biological studies retain Parasponia as a genus because of its unique rhizobial symbiosis, while current Kew taxonomy includes those species in Trema. These differences warrant explicit explanation rather than blending incompatible nomenclatural treatments.
Finally, Rosales and Fabids are not equivalent. Fabids contain Fabales, Rosales, Fagales, and Cucurbitales. The expression nitrogen-fixing clade refers to that broader four-order radiation and does not imply that every Rosalean fixes nitrogen. Most do not. The name instead reflects the unusual evolutionary concentration of root-nodule symbiosis across these four orders.
11. Additional Information
Angiosperm Phylogeny Group V provides the higher-level framework used by Tree TSAR. It retains the nine-family Rosales circumscription while restricting Fabids to Rosales, Fabales, Fagales, and Cucurbitales. The 2026 phylogenomic study by Liu et al. is especially important because it compares nuclear, plastid, and mitochondrial histories across all nine families and demonstrates that incomplete lineage sorting and ancient hybridization are genuine components of Rosalean evolution. The older multi-gene study by Zhang et al. (2011) remains useful as a clear working framework for the broad urticalean and rhamnalean assemblages, but it should no longer be treated as the final word on every family branch.
The Angiosperm Phylogeny Website, Plants of the World Online, and World Flora Online remain essential supporting resources for morphology, nomenclature, accepted genera, family circumscription, and historical classification. The important distinction is between stable classification and unstable topology. The nine living families are secure, while lower-level decisions such as Parasponia versus Trema, generic limits in Rosaceae, or tribal rearrangements in Rhamnaceae can be adjudicated independently without destabilizing the ordinal pathway.
12. References and Further Reading
Angiosperm Phylogeny Group (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. https://doi.org/10.1111/boj.12385 (opens in a new tab)
Angiosperm Phylogeny Group (2026) Large-scale nuclear and plastid phylogenomic analyses inform an updated Angiosperm Phylogeny Group classification: APG V. Journal of Systematics and Evolution 64(5): 845-874. https://doi.org/10.1111/jse.70096 (opens in a new tab)
Doyle JJ, Ren J, Pawlowski K, James EK, Gao Y (2025) One versus many independent assemblies of symbiotic nitrogen fixation in flowering plants. Nature Communications 16: 5345. https://doi.org/10.1038/s41467-025-60433-w (opens in a new tab)
Govaerts R, Nic Lughadha E, Black N, Turner R, Paton A (2021) The World Checklist of Vascular Plants, a continuously updated resource for exploring global plant diversity. Scientific Data 8: 215. https://doi.org/10.1038/s41597-021-00997-6 (opens in a new tab)
Kates HR, O’Meara BC, LaFrance R, Stull GW, James EK, Liu S-Y, Tian Q, Yi T-S, Conde D, Kirst M, et al. (2024) Shifts in evolutionary lability underlie independent gains and losses of root-nodule symbiosis in a single clade of plants. Nature Communications 15: 4262. https://doi.org/10.1038/s41467-024-48036-3 (opens in a new tab)
Li H-T, Luo Y, Gan L, Ma P-F, Gao L-M, Yang J-B, Cai J, Gitzendanner MA, Fritsch PW, Zhang T, et al. (2021) Plastid phylogenomic insights into relationships of all flowering plant families. BMC Biology 19: 232. https://doi.org/10.1186/s12915-021-01166-2 (opens in a new tab)
Liu L, Lv W, Soltis DE, Comes HP, Zhang Y, Shi Y, Li S, Wang M, Gao W, Li S (2026) Complex evolutionary history of Rosales mediated by extensive incomplete lineage sorting and hybridization. Molecular Phylogenetics and Evolution 225: 108716. https://doi.org/10.1016/j.ympev.2026.108716 (opens in a new tab)
Martín JA, Domínguez J, Solla A, Brasier CM, Webber JF, Santini A, Martínez-Arias C, Bernier L, Gil L (2023) Complexities underlying the breeding and deployment of Dutch elm disease resistant elms. New Forests 54: 661-696. https://doi.org/10.1007/s11056-021-09865-y (opens in a new tab)
Stevens PF (2001 onwards) Angiosperm Phylogeny Website. Missouri Botanical Garden, St. Louis. https://www.mobot.org/MOBOT/research/APweb/orders/rosalesweb.htm (opens in a new tab)
Sytsma KJ, Morawetz J, Pires JC, Nepokroeff M, Conti E, Zjhra M, Hall JC, Chase MW (2002) Urticalean rosids: Circumscription, rosid ancestry, and phylogenetics based on rbcL, trnL-F, and ndhF sequences. American Journal of Botany 89(9): 1531-1546. https://doi.org/10.3732/ajb.89.9.1531 (opens in a new tab)
World Flora Online Consortium (2026) Rosales Bercht. & J.Presl. World Flora Online. https://www.worldfloraonline.org/taxon/wfo-9000000467 (opens in a new tab)
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