Macginitiea is an extinct genus in the family Platanaceae ranging from the Late Paleocene to Late Eocene of North America, known from the Clarno Formation of central Oregon.[1][2] The genus is strictly used to describe leaves, but has been found in close association with other fossil platanoid organs, which collectively have been used for whole plant reconstructions.[2][3] Macginitiea and its associated organs are important as together they comprise one of the most well-documented and ubiquitous fossil plants, particularly in the Paleogene of North America.[4][5]
Because paleobotanical material is often found in disarticulation, different species names are often used to refer to different organs (e.g. leaves, fruits, wood) even if those organs might have belonged to the same plant. When these organ species are considered together as a whole plant, the study is known as a whole plant reconstruction. Some localities have enough co-occurrences of different fossil plant organs that whole plant reconstructions are possible, one example being the Cercidiphyllum-like Joffrea from the Joffre Bridge locality of Alberta, Canada.[6]
The earliest definite occurrences of Macginitiea have been observed from the Comstock Flora of southern Willamette Valley, Oregon, which has been dated to be younger than 38-40 million years old (Bartonian), though similar ages are observed throughout the Pacific Northwest, with occurrences around 38-39 Ma.[4]
Macginitiea leaves are readily recognizable by their three to nine, equally spaced, palmate lobes.[2][7] Like other Platanaceae, Macginitiea has palinactinodromous primary venation, a type of venation wherein primary veins fork multiple times. Macginitiea also has an inflated petiole base,[2] which in modern counterparts encloses the underlying axillary buds for the next year, indicating their deciduous nature.[8] The branching of primary veins often occurs basally, rather than suprabasally (as encountered in some modern species).[2] Although the secondary veins of modern Platanus are usually straight, the secondary veins of Macginitiea are so regular and prominent compared to other platanoids that this recognizable "chevron" pattern has been considered a primary characteristic of the species.[2][3][7][9] Margins are usually entire in all Macginitiea species, but can sometimes have minor teeth.[3]
Macginitiea differs from modern Platanus with its often greater number of lobes and narrower angle between adjacent primary veins.[7]
Different species of Macginitiea can be distinguished on the basis of lobe depth, extent of chevrons, prevalence of teeth, and partly lobe number.[3] In total, 5 species of Macginitiea leaves have been described.[2][3][5][7]