Eudicots

The eudicots, also called eudicotyledons, are a group of flowering plants that sprout with two seed leaves, or cotyledons. The name comes from "dicotyledon," with "eu" meaning true, "di" meaning two, and "cotyledon" meaning seed leaf. In the past, these plants were referred to as tricolpates or non-magnoliid dicots. The modern botanical terms were introduced in 1991 by evolutionary botanist James A. Doyle and paleobotanist Carol L. Hotton to highlight that tricolpate dicots evolved later than earlier, less specialized dicots. Many familiar plants are eudicots, including a wide range of cultivated crops, edible plants, trees, tropical species, and ornamentals. Well-known examples include sunflowers (Helianthus), dandelions (Taraxacum), forget-me-nots (Myosotis), cabbage (Brassica), apples (Malus), buttercups (Ranunculus), maples (Acer), and macadamia nuts (Macadamia). Most leafy trees found in mid-latitude regions are eudicots, though magnolias and the American tulip tree (Liriodendron) are exceptions, as they belong to the magnoliids. The close relationships among flowering plants with tricolpate pollen were first noticed through morphological studies of shared traits. These plants have a distinctive pollen feature: three colpi, or grooves, that run parallel to the pollen grain’s polar axis. Later, molecular evidence confirmed the genetic basis for these evolutionary links. The term "eudicots" means "true dicotyledons" because the group includes most plants once considered dicots, sharing typical dicot characteristics. A key genetic trait defining eudicots is the duplication of DELLA protein-encoding genes in their most recent common ancestor. The name "eudicots" has become widely used in botany to describe one of the two largest clades of angiosperms, making up over 70% of all flowering plant species; the other major clade is the monocots. The remaining angiosperms include magnoliids and what are sometimes called basal angiosperms or paleodicots, though these terms are not consistently applied because they do not form a monophyletic group. Molecular clock calculations suggest the lineage leading to eudicots split from other plants about 134 million years ago, or between 155 and 160 million years ago. Fossil evidence shows that basal eudicots were already diverse around 121 million years ago. The older name for eudicots is tricolpates, referring to their pollen’s grooved structure. Members have tricolpate pollen, or forms derived from it, with three or more pores set in furrows called colpi. In contrast, most other seed plants—gymnosperms, monocots, and paleodicots—produce monosulcate pollen, which has a single pore in a differently oriented groove called a sulcus. Some botanists prefer "tricolpates" to avoid confusion with the dicots, a nonmonophyletic group. The name "eudicots" is used in the APG systems (from 1998 to 2016) for classifying angiosperms, referring to a monophyletic clade that includes most former dicots. "Tricolpate" is a synonym for this group, the true dicotyledons, distinguished by their tricolpate pollen. The number of furrows or pores in pollen helps classify flowering plants: eudicots have three colpi, while other groups have one sulcus. Pollen apertures are modifications of the pollen grain wall, including thinning, ridges, and pores, which allow the pollen contents to exit and help the grain shrink and swell with moisture changes. The elongated furrows are called colpi, and along with pores, they are key for identifying pollen classes. Eudicots can be split into two groups: basal eudicots, an informal paraphyletic group, and core eudicots, a monophyletic group. A 2010 study suggested core eudicots divide into two clades: Gunnerales and Pentapetalae, which includes all remaining core eudicots. Pentapetalae then splits into three clades: Dilleniales; superrosids (containing Saxifragales and rosids, with Vitales included in rosids under APG IV); and superasterids (containing Santalales, Berberidopsidales, Caryophyllales, and asterids).