Plant taxonomy arranges the over 300,000 species of plants on Earth into a nested hierarchy based on shared evolutionary ancestry and genetics (how related they are) as well as morphological features, which is how we used to always define them. By categorizing life into broad groups and systematically narrowing them down, plant taxonomy creates a clear framework that allows us to understand how different plants are related.
Sometimes the morphology makes those relationships obvious, but morphology alone left us with many unanswered questions and the lumping of unrelated taxa together in polyphyletic groups (they don’t share a common ancestor). This is why we sometimes require molecular phylogenetics, the branch of evolutionary biology that analyzes DNA, RNA, and protein sequences to determine evolutionary relationships and ancestral branching among organisms. Molecular phylogenetics has in some cases radically redefined how we view plant taxonomy classifications, and I will note below when there have been major changes.
Kingdom Plantae
All plants belong to the plant kingdom, also called “Plantae,” which covers all multicellular green plants that produce their own food via photosynthesis (or have adapted non-photosynthetic parasitism). They also have rigid cell walls made of cellulose and include everything from microscopic mosses to giant sequoia trees.
Phylum / Division
“Division” and “phylum” are two words for the same thing, and in plants, you may see both used. Either way, these are the major lineages of the kingdom. While there are more, you will generally see most plants broken into 4 main phyla:
Bryophyta are the non-vascular land plants, the most primitive land plants, which include mosses, liverworts, and hornworts.
Pteridophyta are the most primitive vascular plants that do not produce seeds but use spores instead. These include ferns and horsetails.
Gymnosperms are called “naked seed” plants because their seeds are not enclosed in any kind of fruit; fruits come from flowers, and gymnosperms do not produce flowers. These are conifer trees, cycads, and gingkos.
Angiosperms are the flowering plants that most of us probably think of when we think of plants. They may be trees, shrubs, vines, or herbs, but they all produce flowers, and their seeds are enclosed in fruits formed from ovaries.
Class
Divisions are then subdivided into classes, which group plants by core structural developments. Historically there were two main classes of flowering plants that were widely used to group species.
Monocots or Liliopsida have seeds with embryos that produce a single seed leaf (cotyledon) and have parallel leaf veins, and floral parts usually in multiples of three (lilies, orchids, grasses, etc.)
Dicots/Eudicots, or Magnoliopsida, are characterized by having embryos with two seed leaves, net-like (pinnate, palmate, etc.) leaf veins, and floral parts in multiples of four or five (roses, sunflowers, oak, etc.).
However, there are still others that don’t fit in these two classes, and modern phylogenetics prefers the use of clades instead to reflect evolutionary relationships. Still, here we divide our angiosperms based on dicots, monocots, and basal or mesangiosperms, who do not fit in the other two classes, simply because there are a lot of angiosperms and this site is intended as an introduction without needing to know evolution, and the classes are something many people have already heard of at some point.
Order
Classes are then broken down into orders, which connect high-level traits to distinct plant families. All plants in the same order share distinct genetic lineages, flower structures, and developmental traits.
Note about this site: I have categorized the plant families into orders, and once I cover enough different orders, I will create order pages. But for now, I provide an overview of all the major plant orders found anywhere in the American continents, from Canada south to Patagonia. I know I have skipped a few small, largely tropical orders for now, but I will add those at a later date, as I also have no photos of any of the families in those orders (the tropics are on my bucket list!). Furthermore, you may notice I have not added the bryophyte and pteridophyte orders on purpose, as they will be the last ones added to the site once I do the flowering plants and gymnosperms.
Gymnosperm Orders in Plant Taxonomy
Cupressales
The Cupressales are a major order of coniferous gymnosperms ranging from low alpine shrubs to massive giant trees. They typically have diminutive, tightly appressed scale-like leaves or awl- or needle-like leaves, and they produce terpene-rich resins and shield-shaped woody or leathery cones, or sometimes berry-like cones (as in Juniperus). Two major families are Cupressaceae (cypress) and Taxaceae (yews). Many sources will still list members under a larger Pinales order, but modern plant taxonomy based on molecular phylogenetics has separated them as their own monophyletic group.
Cycadales
The Cycadales are an ancient order of seed plants that dates back over 280 million years, one of the earliest lineages to diverge from the ancestral seed-bearing plants. They resemble palms or ferns, but they do not flower and exhibit strictly dioecious reproduction via large, woody strobili (cones) instead of flowers or fruits. They also share swimming sperm with Gingko, unique among the seed plants. The families are the Cycadaceae (cycads) and Zamiaceae (zamia family).
Ginkgoales
The Ginkgoales are another ancient order, 270 million years old, containing a single surviving family, Ginkgoaceae, and a single surviving species, Ginkgo biloba. While native to eastern China, it is now widely planted in urban environments around the world for its hardiness. It is a dioecious tree with fan-shaped leaves that have dichotomous venation and fleshy, malodorous seeds resembling fruits, and it shares unique mobile sperm with cycads, the only other surviving seed plants that have this trait.
Gnetales
The Gnetales are a unique lineage of three distinct families, the Ephedraceae (Mormon tea), Gnetaceae (gnetum), and Welwitschiaceae (welwitschia), which range from photosynthetic jointed desert shrubs and broad-leaved tropical vines to desert succulents that contain true vessel elements like those of angiosperms and unlike any other gymnosperm. They produce flower-like compound strobili with flower-like bracts that produce nectar, and they exhibit a primitive form of double fertilization but do not produce the endosperm of a true angiosperm. Leaves are opposite or whorled and often reduced to papery sheaths.
Pinales
The Pinales are the largest order of the gymnosperms with about 230 species in a single family, the Pinaceae. They are woody shrubs and trees with needle-like leaves in clustered fascicles (as in Pinus) or in flat two-ranked arrays on short shoots (as in Abies). They have woody compound seed cones and rely on wind pollination. They also possess resin ducts in their trunks, leaves, and bark with sticky terpenes as defense against pests and pathogens.
Monocot Orders in Plant Taxonomy
Acorales
The Acorales are a basal monocot, one of the earliest diverging lineages, consisting of a single family, the Acoraceae, and a single genus, Acorus, which are semi-aquatic, aromatic perennial herbs known as sweet flags. They have tiny flowers densely packed on a cylindrical spadix. The spadix is why they were previously placed in the Alismatales order in the Araceae, or arum, family, but molecular phylogenetics confirmed that Acorus is a sister to all other living monocots and was elevated to its own order.
Alismatales
The Alismatiles are an ancient and diverse order of monocots that diverged from the rest just after the Acorales and includes almost all of the world’s freshwater aquatic angiosperms and marine seagrasses. A key trait is their intravaginal scales, tiny structures inside the leaf sheaths that secrete mucilage to protect the growing tips. Flowers are variable, but the gynoecium usually features free, unfused carpels (apocarpous). This group includes families like Araceae (arum), Alismataceae (water plantain), Potamogetonaceae (pondweed), Zosteraceae (sea grasses), Tofieldiaceae (false asphodel), and others.
Arecales
The Arecales are a major monocot order within the commelinid clade containing a single family, Arecaceae, or the palm family, which is economically and ecologically one of the most important flowering plant families on Earth. They are mostly woody, unbranched “trees” and climbing vines that lack true secondary growth like most trees and have distinctive large evergreen leaves clustered in a dense crown at the top of the stem, making them more akin to giant herbs than woody forest trees. Flowers are small but often borne in large, highly branched inflorescences and produce 1-seeded drupes or berries.
Asparagales
The Asparagales are the largest and most diverse monocot order of mostly herbaceous perennials that survive winter or dry seasons via underground storage roots. Seeds typically possess a black, crusty outer seed coat called phytomelanin (but may be lost in fleshy-fruited species). Several woody lineages like Agave, Yucca, and Dracaena also exhibit anomalous secondary thickening, allowing them to form tree-like trunks without true wood. It includes major families like Orchidaceae (orchids), Amaryllidaceae (amaryllis), Asparagaceae (asparagus, yucca), Iridaceae (iris), and more. Under older plant taxonomy classifications, many were previously lumped in the very heterogeneous Liliales order, but they have been designated as a distinct, massive monophyletic order.
Commelinales
The Commelinales are a well-defined monocot order of herbaceous perennials, aquatic plants, and colorful herbaceous wildflowers. The order is characterized by plant cell walls containing ferulic acid derivatives that fluoresce under UV light. Flowers are 3-merous, usually with 3 petals and 3 sepals, and stamens are often densely covered in colorful hairs. Major families include the Commelinaceae (spiderwort), Pontederiaceae (water hyacinth), Haemodoraceae (bloodwort), and others.
Dioscoreales
Dioscoreales are an ancient order of monocots made of massive climbing vines to achlorophyllous mycoheterotrophic herbs, characterized by large underground storage organs, net-veined leaf blades (rare in monocots), and the presence of steroidal saponins and toxic alkaloids. Families include the Dioscoreaceae (yam), Nartheciaceae (bog ashpodel), Burmanniaceae (burmannia), and others. Historical plant taxonomy often placed members in the Liliales or near the Orchidaceae, but modern phylogenetics has established it as a distinct basal order, sister to the Pandanales.
Liliales
The Liliales are a large group of monocots characterized by geophyte storage organs, petaloid tepals with nectaries, often with patterns or spots to guide pollinators, and extrorse anthers. Major families include the Liliaceae (lilies), Smilaceae (greenbriar), Melanthiaceae (bunchflower), and others. Historically, plant taxonomy used this order as another catch-all for any monocot with 6 showy petals and superior ovaries. However, under APG IV, it was reduced and now is a tight monophyletic order, sister to the Asparagales and Commelinids.
Poales
The Poales are a massive, ecologically dominant order of commelinid monocots, with 14 families and about one-third of all monocots. They have linear, strap-like leaves with parallel veins and basal sheaths that enclose the stems and possess widespread C4 carbon fixation lineages adapted to arid and high-light environments. Major families include the Poaceae (grass), Cyperaceae (sedge), Juncaceae (rush), Bromeliaceae (pineapple), and others.
Basal Angiosperm and Mesangiosperm Orders in Plant Taxonomy
Austrobaileyales
The Austrobaileyales are a small order with only about 100+ species, but they are one of the earliest diverging lineages of angiosperms that predate monocots and dicots, often called the ANA grade (named after the 3 orders: Amborellales, Nymphaeales, and Austrobaileyales). They are known for stems and leaves that have specialized spherical oil cells that are often aromatic; primitive xylem, reflecting early stages in vessel element evolution; and flowers that are often solitary, spirally arranged, and made of tepals, with leaf-like stamens and unfused carpels. Major families include the Schisandraceae (star-vines and the former Illiciaceae) and the Austrobaileyaceae (Austrobaileya).
Canellales
The Canellales are an ancient order of woody plants in the magnoliid clade, neither a dicot nor a monocot, placed at the base of the “mesangiosperm” tree. They are characterized by their aromatic chemistry and pungent bark; the lack of vessel elements in their xylem, a testament to their primitive ancestry; and flowers that are spirally or whorled with undifferentiated perianth parts and leaf-like or fused stamens. The Canellaceae (wild cinnamon) and Winteraceae (winter’s bark) are the two major families.
Ceratophyllales
The Ceratophyllales are a small but important order of mesangiosperms consisting of a single family, the Ceratophyllaceae, and a single genus (Ceratophyllum) known as “hornworts” or “coontails,” a globally distributed group of submerged freshwater aquatic plants that are rootless and free-floating, anchored to the substrate with root-like leaves, and exhibit underwater pollination and small, hard, single-seeded achene fruits with a terminal spine and two basal spines. Historical plant taxonomy based on morphology found it difficult to place because of its drastically reduced anatomy for underwater life. But now it is recognized as an isolated lineage, an early-diverging sister group to the dicots.
Chloranthales
The Chloranthales are a major independent lineage, one of the earliest diverging lineages of the mesangiosperms, sister to the magnoliids, and consist of a single family, the Chloranthaceae (Chloranthus). They possess highly primitive, minute flowers that usually lack a perianth and have stamens fused directly to the 1-carpelled ovary. Leaves are opposite, simple, and aromatic, with small glandular tips on their serrated margins and the leaf petioles uniting into a distinct sheathing stipular cup. Many are rich in essential oils and emit a spicy or pine-like fragrance when crushed.
Laurales
The Laurales are a group of basal angiosperms that are sister to the Magnoliales. It is mostly made of woody trees, shrubs, and vines with aromatic oil cells, giving members a strong spicy or herbal scent when crushed. They are characterized by having anthers dehisce along 2 or 4 flap-like upward-curling valves, trimerous flowers with cup-like receptacles, and mostly producing single-seeded drupes or berries. Major families include the Lauraceae (laurel, avocado), Calycanthaceae (spicebush, sweet shrub), Hernandiaceae (hernandia), and others.
Magnoliales
The Magnoliales are another ancient order of basal angiosperms, of the magnoliid clade and sister to the Laurales. They are woody trees, shrubs, and large woody vines with flowers that have a prominent receptacle column, with spirally arranged carpels and stamens attached in whorls, with tepals arranged spirally or in multiples of three, and with stamens that are flat, laminar, and lack distinct filaments. They often emit strong spicy fragrances when crushed. Major families include the Annonaceae (custard apple), Magnoliaceae (magnolia), Myristicaceae (nutmeg), and others.
Nymphaeales
The Nymphaeales are one of the most primitive, early-diverging angiosperms, made of freshwater aquatic, rhizomatous flowering herbs belonging to the ANA grade. They have laminar stamens, spirally arranged floral organs, and lack distinct vessel elements in their xylem. Leaves are peltate or cordate and float on the water surface, and flowers are solitary and showy. There are three families that include Cabombaceae (water-shield), Hydatellaceae (hydatella), and Nymphaeaceae (water lily).
Piperales
The Piperales are an early-diverging angiosperm in the magnoliid clade, sister to the Canellales. The three families include the Piperaceae (pepper) and Saururaceae (lizard’s tail), as well as the Aristolochiaceae (birthwort), which was historically classified in its own order. The Piperales are woody shrubs and vines, epiphytes, perennial herbs, and aquatic plants with aromatic ethereal oils yielding pungent, spicy, or anise-like scents. Inflorescences are mostly minute and apetalous but densely packed in characteristic elongated, often rat-tail-like spikes or spadices, except for the fleshy, often petaloid, united sepals of the Aristolochiaceae.
Proteales
Proteales are an ancient dicot lineage that includes diverse riparian trees, floating aquatic herbs, and woody shrubs, characterized by specialized lateral rootlets (proteoid roots) that secrete organic acids to mobilize inorganic phosphorus, as well as apocarpous or monocarpous ovaries that produce follicles, achenes, or round syncarps. The 4 families include Platanaceae (plane trees), Nelumbonaceae (lotus), Proteaceae (macadamia), and Sabiaceae (sabia). In older classifications they were often spread across unrelated orders, but molecular phylogenetics showed that these diverse plants are a monophyletic order of basal dicots.
Dicot Orders in Plant Taxonomy
Apiales
The Apiales are a major dicot order often called the carrot order after the Apiaceae, or carrot family. They typically have small, 5-merous flowers that are usually arranged in flat-topped or spherical umbels (often compound) or heads. The stems, leaves, and roots are often highly aromatic and may be delicious or deadly poisonous. Leaves are mostly deeply divided and fern-like or compound and feature distinct sheathing bases. Fruits are two-seeded shizocarps. Major families include the Apiaceae (carrot), Araliaceae (ginseng), and others.
Aquifoliales
The Aquifoliales are an order of woody flowering dicots, mostly trees and shrubs with simple leathery leaves that often have spiny, dentate, or serrated margins, the most famous of which are the “hollies.” Flowers are small and often unisexual, and fruits are almost always fleshy drupes with multiple single-seeded pyrenes. The Aquifoliceae (holly) contains most of the species, but there are also the Phyllonomaceae (Phyllonoma) and others.
Asterales
The Asterales are a massive order representing about 10% of all flowering plants, dominated by the Asteraceae, or sunflower family, but other notable members include the Campanulaceae (bellflower) and Menyanthaceae (bogbean). They are characterized by their composite flower heads (capitula) that look like a single flower but are in fact made of dozens to hundreds of different smaller flowers, typically called florets. The anthers form a tight tube around the style, which pushes the pollen out as it grows before its own stigmatic surface becomes receptive (protandry).
Berberidopsidales
The Berberidopsidales are a small dicot order of just 3 genera of evergreen woody vines and scrambling shrubs with flowers that feature a continuous transition between sepals and petals (often referred to as tepals or a graded perianth) and fruits that are usually fleshy berries. The families include Berberidopsidaceae (coral plant) and Aextoxicaceae (olivillo). Historically, its members were scattered across unrelated families (Flacourtiaceae and Euphorbiaceae), but modern plant taxonomy using molecular phylogenetics demonstrated that they form a strongly supported monophyletic group.
Boraginales
The Boraginales are a diverse order of dicots that includes herbs and large tropical trees but are often characterized by hispid hairs, coiled, one-sided cyme (scorpioid) inflorescences, 5-merous actinomorphic flowers fused at the base, and a 2-carpel ovary that often splits into four 1-seeded nutlets at maturity. Major families include the Boraginaceae (borage), Cordiaceae (geiger tree), Ehretiaceae (Ehretia), Heliotropiaceae (heliotropes), and Hydrophyllaceae (waterleaf).
Brassicales
The Brassicales (formerly Capparales) is a major dicot lineage that includes critical food crops, herbs, oilseeds, and tropical woody shrubs. The primary uniting feature in the order is the presence of glucosinolates (mustard oil glucosides) used as a chemical defense against herbivores as well as their 4-merous flowers with 4 sepals and 4 petals typically arranged in a cross-like pattern. They also often have tetradynamous stamens, with four long and two short stamens. Fruits are usually specialized capsules called siliques and silicles. Major families include the Brassicaceae (mustard), the Capparaceae (capers), Cleomaceae (spiderflower), Koeberliniaceae (allthorn), Caricaceae (papaya), and others.
Buxales
The Buxales are a small distinct order of dicots made of evergreen shrubs, small trees, and creeping rhizomatous ground covers positioned near the base of the dicot lineage. They accumulate distinct bitter alkaloids as chemical defenses, and their flowers are small and reduced, lacking true petals (apetalous) or having small sepal-like tepals. Leaves are simple and leathery, arranged oppositely or in whorls, and fruits are usually 3-locular, woody capsules. There is only one family, the Buxaceae, or Boxwood family.
Caryophyllales
The Caryophyllales are a massive dicot order famous for extremophytes—plants adapted to harsh, arid, saline, or nutrient-poor soils across the world, often relying on C4 and CAM photosynthesis, succulence, and halophytic tolerance. The vast majority of families synthesize betalain pigments instead of anthocyanins for coloration, unique in the angiosperms. Seeds typically have a curved embryo around a specialized starch-rich storage tissue rather than true endersperm. Flowers typically have free petals and a 1-locular ovary. Major families include the Cactaceae (cactus), Caryophyllaceae (pink, carnation), Amaranthaceae (amaranth), Polygonaceae (knotweed, buckwheat), and others.
Celestrales
The Celestrales are an order of woody trees, shrubs, and vines with seeds containing fleshy, brightly colored arils or seed coats, often in orange, red, or yellow, to attract birds for dispersal. Flowers are unusually small and contain fleshy nectar discs, and fruits are mostly 3- to 5-locular woody capsules, drupes, or berries. The two families are the Celastraceae (bittersweet) and Lepidobotryaceae. Historical plant taxonomy used to use this order as a bit of a catch-all group for loosely related woody families like the Aquifoliaceae and others, but it is now more narrowly defined based on genetic evidence.
Cornales
The Cornales are an early-diverging order of dicots made of woody trees, shrubs, vines, and perennial herbs with an inferior or semi-inferior ovary topped by an epigynous fleshy nectar disc around the base of the style. Several lineages also have petaloid bracts in their inflorescences, while the true flowers are small and tightly clustered. Leaves are mostly opposite and simple, featuring distinct arcuate (curved) secondary leaf veins that arch towards the tip, and when you pull a leaf apart, it reveals elastic thread-like vascular strands. Families include the Cornaceae (dogwood), Hydrangeaceae (hydrangea), Loasaceae (blazing star), and others.
Cucurbitales
The Cucurbitales are another major dicot order, this one made of mostly herbaceous or woody vines climbing via tendrils originating at leaf nodes or shrubs and trees. They mostly have unisexual flowers (dioecious and monoecious) and an inferior ovary that produces a modified multi-seeded berry with a hard, leathery rind known as a pepo (think cucumber or squash). Major families include the Cucurbitaceae (cucumber and squash), Begoniaceae (begonias), Datiscaceae (datisca), and others.
Dilleniales
The Dilleniales consists of a single family, the Dilleniaceae (guinea flower), a group of woody trees, shrubs, and climbing vines with papery, reddish, or brown bark that peels or shreds in distinct strips. They have simple, alternate leaves with distinct straight-parallel secondary veins to produce a ribbed surface texture and flowers with numerous free prominent stamens and fruits that are often dehiscent follicles with red or white fleshy arils or berry-like fruits enclosed by persistent sepals. Historical plant taxonomy also had difficulties placing this group, often placing it near Magnoliaceae, but under APG IV it is recognized as an isolated basal dicot.
Dipsacales
The Dipsacales are a group of woody shrubs, vines, small trees, and herbaceous perennials with opposite leaves, no stipules, capitate or cymose inflorescences, and flowers with fused petals and an inferior ovary. The major families are the Viburnaceae (Adoxaceae in some classifications) and Caprifoliaceae (honeysuckle). Historical plant taxonomy placed some Viburnaceae members in Caprifoliaceae, but their species diverged early, so they were separated. Also, while APG still lists Adoxaceae, Viburnaceae is the currently accepted name.
Ericales
The Ericales are a massive dicot order containing about 22 families ranging from towering rainforest trees and carnivorous pitcher plants to acid-loving heath shrubs and achlorophyllous herbs, often adapted to nutrient-poor or waterlogged soils. Flowers typically have fused petals, and stamens typically number twice the petals. Major families include the Ericaceae (heath), Sarraceniaceae (pitcher plants), Polemoniaceae (phlox), Primulaceae (primula), and more. Historical plant taxonomy defined it much more narrowly, but APG IV drastically expanded it based on molecular phylogenetics.
Fabales
The Fabales are one of the largest and most ecologically dominant and economically important dicot orders. It is comprised of woody trees, vines, and shrubs as well as perennial herbs. They are best characterized by their ability to fix nitrogen in root nodules in association with Rhizobium soil bacteria. They tend to have alternate compound leaves with swollen bases and possess characteristic fruits called legumes (beans and peas!). The four families include the Fabaceae (legumes), Polygalaceae (milkwort), Suriancaeceae (bay cedar), and Quillajaceae (soap bark). Older plant taxonomy records sometimes split the Fabaceae into separate families and placed Polygalaceae in its own order, but DNA sequencing has confirmed the current Fabales as a monophyletic order.
Fagales
The Fagales are woody dicots with small apetalous and unisexual flowers, typically grouped in drooping cylindrical catkins for wind pollination. They produce true single-seeded, hard-shelled nuts or samaras, partially or completely enclosed in leafy or woody cupules, and nearly all form symbiotic relationships with ectomycorrhizal fungi. Major families include the Fagaceae (beech and oak), the Betulaceae (birch and alder), Myricaceae (wax myrtle), and others.
Garryales
The Garryales are a small order of woody shrubs, small trees, and vines that are strictly dioecious (male and female flowers on separate plants) with small apetalous flowers born in catkin-like spikes or racemes for wind dispersal. Leaves are simple, evergreen, leathery, and oppositely arranged, often with connate petiole bases that form a ridge across the stem node. There are only two small families, the Garryaceae (silk tassel) and the Eucommiaceae (hardy rubber tree).
Gentianales
The Gentianales are a massive dicot order with over 20,000 species of trees, woody vines, and diverse herbs with simple, entire, and opposite leaves with interpetiolar stipules; 4- to 5-merous flowers with fused petals; and tissues that exude potent iridoid glycosides and indole alkaloids and often contain laticifers that exude milky latex. The five families include the Apocynaceae (dogbane and milkweed), Gelsemiaceae (jessamine), Gentianaceae (gentian), Loganiaceae (strychnine), and Rubiaceae (madder and bedstraw). Under older plant taxonomy descriptions, it was defined more narrowly, often separating Rubiaceae for its inferior ovary, but modern phylogenetics and the presence of things like indole alkaloid chemistry have established it as a larger monophyletic order.
Geraniales
The Geraniales are a small but widespread order of dicots made of two families, the Geraniaceae (geraniums) and the Francoaceae (bridal wreath). They are characterized by a superior ovary with a prolonged central column (rostrum or beak) that splits in 5 1-seeded mericarps that often catapult away from the parent plant. They also have predominantly palmately lobed leaves, aromatic glandular hairs, 5-merous flowers with 5-10 stamens, and nectary glands. Older plant taxonomy classifications used this order as a heterogenous catch-all for families like the Balsaminaceae, Oxalidaceae, and others, but it was streamlined by molecular phylogenetics, which defines it more narrowly.
Gunnerales
Gunnerales are a small order that sits as the most basal lineage of core dicots with two families, the Gunneraceae (gunnera) and Myrothamnaceae (resurrection plant). They range from giant-leaved herbaceous perennials to delicate woody trees and shrubs with primitive, mostly apetalous flowers arranged in large spike-like or panicle inflorescences up to 2 m tall.
Lamiales
The Lamiales are a huge, diverse order with about 24 families and over 24,000 species, including aromatic herbs, woody trees, vines, carnivorous aquatics, and root parasites. They typically have zygomorphic two-lipped flowers, diandrous or didynamous stamens, opposite leaves, square stems, and often have glandular, aromatic trichomes and essential oils. Some major families include the Lamiaceae (mints), Scrophulariaceae (figwort and snapdragon), Plantaginaceae (plantain), Acanthaceae (acanthus), and others. In historical plant taxonomy, Lamiales was much more narrowly defined, while those with capsular fruits were placed in Scrophulariales, but molecular phylogenetics urged a merging of those orders, greatly expanding Lamiales.
Malpighiales
The Malpighiales are a large, ecologically and morphologically diverse order spread across about 35 families and include trees, mangrove shrubs, woody vines, and herbs. They are mostly characterized by the lack of unifying morphological synapomorphy, relying instead on shared molecular and anatomical markers. Major families include the Euphorbiaceae (spurge), Malpighiaceae (acerola), Violaceae (violet), and others. With the lack of unifying characteristics, unsurprisingly, older plant taxonomy records classified the families across widely different orders, many of which have now simply been merged into the new monophyletic Malpighiales order.
Malvales
The Malvales are a large, distinctive order of 10 families of trees, fibrous shrubs, and herbs characterized by having stamens fused into a staminal column that surrounds the style. They also typically are densely covered in stellate or peltate–scale hairs, have tissues with abundant mucilage, and have stems with tough, fibrous phloem strands that make them useful for rope-making. Major families include the Malvaceae (mallows), Cistaceae (rockrose), Thymelaeceae (mezereum), and others. Historical plant taxonomy classifications defined Malvales and the Malvaceae much more narrowly, but molecular phylogenetics showed this new broader definition to be monophyletic.
Myrtales
The Myrtales are a large order spread across 9 families of trees, shrubs, and wetland herbs characterized by a tube- or cup-shaped hypanthium with sepals, petals, and stamens attached on the rim and simple, entire, opposite leaves that are often aromatic. Flowers are predominantly 4-merous with 4 sepals, 4 petals, and often 8 stamens in 2 whorls. Major families include the Myrtaceae (myrtle), Onagraceae (evening primrose), Lythraceae (loosestrife), Combretaceae (white mangrove), and others.
Oxalidales
The Oxalidales are a medium-sized order with 7 families of clover-like herbs, trees, carnivorois plants, and woody vines with leaves that are mostly compound and often exhibit nyctinasty via swollen petiole bases (pulvini). Flowers are 5-merous with 5 distinct sepals and petals and 10 stamens in 2 whorls, often with varying style and stamen length. Major families include the Oxalidaceae (wood sorrel), Eleocarpaceae (elaeocarpus), Brunelliaceae (brunellia), and others.
Picramniales
The Picramniales are a small, distinct order of dicots consisting of one family, the Picramniaceae (bitterbush), endemic to the tropical and subtropical Americas. They are dioecious woody shrubs and trees characterized by alternate, pinnately compound leaves; small 3- to 6-merous flowers borne in elongate, pendulous racemes, spikes, or panicles; and fleshy berries or samaras. Previously, the order was placed within the Simaroubaceae family and the Sapindales order until it was discovered that it is a separate lineage sister to the Malvids.
Ranunculales
The Ranunculales are a relatively large order of the earliest lineage of true eudicots (plants with tricolpate pollen grains), made of mostly woodland herbs, vines, and woody understory shrubs characterized by having numerous stamens and multiple free unfused carpels arranged spirally or in whorls on an elongated receptacle. Flower parts are often tepals or feature inner whorls of petals modified into tubular, spurred, or cup-like nectary glands. Major families include the Ranunculaceae (buttercups), Papaveraceae (poppies), Berberidaceae (barberry), and more. Historical plant taxonomy often classified them with the Magnollids due to having apocarpous carpels and numerous stamens.
Rosales
The Rosales is one of the most well-known orders for its countless fruit trees (plums, cherries, apples, etc.), berries (strawberries, blackberries, and raspberries), and ornamentals (roses). They are characterized by having 5-merous flowers with numerous stamens and a well-developed hypanthium and leaves that almost universally have paired stipules at their base. Major families include the Rosaceae (roses, apples), Ulmaceae (elms), Moraceae (mulberry), Urticaceae (nettles), and more. Historically, the Rosales were a broad catch-all group that was both narrowed and expanded under APG IV.
Santalales
The Santalales are a highly distinct order of dicots famous for their parasitic lifestyle, from facultative root hemiparasitic herbs and trees to obligate aerial stem hemiparasites (mistletoes) and non-photosynthetic holoparasites. Almost all members are characterized by having haustoria, specialized invasive root/stem connections used to siphon water, nutrients, and carbohydrates from their host. They also produce single-seeded drupes or berries with a very sticky mucilage that glues onto host bark via bird dispersal. Major families include the Santalaceae (sandalwood), Loranthaceae (showy mistletoe), and others.
Sapindales
The Sapindales are a large, important order of almost entirely woody trees, shrubs, and vines famous for resinous bark, volatile essential oils, citrus fruits, and major forest hardwoods. Leaves are mostly alternate and odd-pinnate or palmately compound or lobed and typically lack stipules. Flowers are small, 4-5-merous, and have a prominent intrastaminal or extrastaminal nectary disc surrounding the ovary base. Major families include the Sapindaceae (soapberry), Rutaceae (citrus), Anacardiaceae (cashew, sumac), and others.
Saxifragales
The Saxifragales are a diverse order with 15 families and a wide range of growth forms from succulent herbs and alpine herbs to massive trees, woody vines, and aquatic herbs. They are characterized by typically having ovaries with 2+ carpels fused basally but diverging at the tip, forming a two-horned capsular structure; they have well-developed hypanthiums, 5-merous flowers, and often feature twice as many stamens as petals. Major families include Saxifragaceae (saxifrage), Crassulaceae (stonecrops), Grossulariaceae (gooseberry), and others. Historical plant taxonomy classifications used this order as another catch-all for lumping unrelated families with similar hypanthiums and ovaries, but they were split out under APG IV.
Solanales
The Solanales are a major order of mostly herbs, vines, subshrubs, and shrubs characterized by having fused petals, superior ovaries, and alternate leaves without stipules. They also produce complex tropane and steroidal alkaloids, which make many of them potent poisons and medicines, while many are important agricultural crops (peppers, tobacco, and ornamentals). Major families include the Solanaceae (nightshades), Convolvulaceae (morning glories), Hydroleaceae (hydrolea), and others.
Vitales
The Vitales is an ancient, distinct order of core dicots made of a single family, the Vitaceae (grapes), mostly made of woody vines with tendrils, swollen nodes, and succulent berries with pear-shaped seeds. Historical plant taxonomy placed the Vitales in the Rhamnales based on their 4-5-merous flowers and stamens that are opposite the petals. However, APG IV recognizes it as an independent order, the earliest-diverging lineage of the rosid cuperclade.
Zygophyllales
The Zygophyllales is a small, distinct order with two families, the Zygophyllaceae (caltrop) and the Krameriaceae (ratany). They are mostly drought-tolerant herbs, shrubs, trees, and root parasites with thick resinous cuticles, water-storing parenchyma, or special metabolic pathways tailored for drought and salinity tolerance. They are also characterized by having abundant calcium oxalate crystals in the stems and leaves, having dense resins, and having varied flowers. Historical plant taxonomy placed the two families in unrelated orders, but molecular phylogenetics showed they share a common ancestor.
Additional Information and References
- Visit Lyrae’s Dictionary of Botanical Terms to learn the terminology of botanists. Note that if you hover over most of the words in the articles, you can also get definitions from them there.
- POWO (2019+). Plants of the World Online. Facilitated by the Royal Botanic Gardens, Kew. Published on the Internet: http://www.plantsoftheworldonline.org/ *This is the best source in general for easy species research, although it can depend on the family.
- Stevens, P. F. (2001+). Angiosperm Phylogeny Website. Version 14, July 2017 [more or less continuously updated since]. http://www.mobot.org/MOBOT/research/APweb/ **This is the authoritative source for orders and families, outside of newly published scientific journals.
- WFO (2022): World Flora Online. Published on the Internet: http://www.worldfloraonline.org. Accessed Spring 2022 – current
