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
Flowering plant seed plants and later angiosperms appears to be the result of two distinct rounds of whole genome duplication events. These occurred at and . Another possible whole genome duplication event at perhaps created the ancestral line that led to all modern flowering plants. That event was studied by sequencing the genome of an ancient flowering plant, "Amborella trichopoda", and directly addresses Darwin's ""abominable mystery"." The earliest known macrofossil confidently identified as an angiosperm, "Archaefructus liaoningensis", is dated to about 125 million years BP (the Cretaceous period), whereas pollen considered to be of angiosperm origin takes the fossil record back to