Flowering plant magnoliid (2%) clades. The remaining 5 clades contain a little over 250 species in total; i.e. less than 0.1% of flowering plant diversity, divided among 9 families. The 43 most-diverse of 443 families of flowering plants by species, in their APG circumscriptions, are Of these, the Orchidaceae, Poaceae, Cyperaceae, Araceae, Bromeliaceae, Arecaceae, and Iridaceae are monocot families; Piperaceae, Lauraceae, and Annonaceae are magnoliid dicots; the rest of the families are eudicots. Double fertilization refers to a process in which two sperm cells fertilize cells in the ovule. This process begins when a pollen grain adheres to the stigma of the
Species Plantarum of the thousands of plant species known to Linnaeus at the time. In the first edition, there were 5,940 names, from "Acalypha australis" to "Zygophyllum spinosum". In his introduction, Linnaeus estimated that there were fewer than 10,000 plant species in existence; there are now thought to be around 400,000 species of flowering plants alone. The species were arranged in around a thousand genera, which were grouped into 24 classes, according to Linnaeus' sexual system of classification. There are no descriptions of the genera in '; these are supplied in the companion volume ' ("the genera of plants"), the fifth edition