Platanaceae

Platanaceae, also called the plane family, is a group of flowering plants. It belongs to the order Proteales and has only one living genus, Platanus, with twelve known species. These plants grow into tall trees and are found in temperate and subtropical areas of the Northern Hemisphere.

One of the most famous members of this family is the hybrid London plane, which is commonly planted in cities around the world. These trees are known for their strength and ability to thrive in urban environments.

Description

Plane trees are large, tall trees with bark that peels off in big, uneven sheets, leaving a smooth, pale surface. The bark at the bottom of the trunk stays intact. These trees have leaves that come in many shapes, often with lobes or teeth along the edges.

The flowers are small and not showy, with separate male and female flowers on the same tree. They grow in clusters and produce fruit that is grouped together in round clusters, surrounded by long hairs. The seeds are small and have little stored food for growth.

Ecology

The trees in the Platanaceae family bloom in the spring when new leaves start to grow. Their flowers are spread by wind, and the fruit usually falls in autumn after it has ripened.

These trees like cool, temperate places and are often found near rivers and streams. They do not grow in very dry or extremely cold areas.

Phytochemistry

These trees have special compounds inside them, like cyanogenic glycosides that come from tyrosine, and flavonoids such as prodelphinidin and flavonols like kaempferol, quercetin, and myricetin. They also contain triterpenols, including betulinic acid. However, they do not have ellagic acid, saponins, or sapogenins.

Cultivation

Many of these trees are planted to give shade in places where people walk, especially in cooler areas. The London plane, found across Europe and North America, is very strong and healthy, likely because it is a mix of two types of trees. However, care is needed because these trees can produce tiny particles that may cause allergies. The wood from these trees is also used to make beautiful furniture and walls, and it burns for a long time.

Fossils

Many old remains of this plant family have been found from a time called the Lower Cretaceous, which was about 98 to 113 million years ago. These ancient plants had small pollen and special leaf shapes, and scientists believe they were pollinated by insects. Later, during the mid Cretaceous period, different leaf shapes appeared and continued until a time called the Eocene. By the Palaeocene period, about 60 million years ago, leaves similar to modern ones became common. The only plant genus we have today, Platanus, is thought to be a special survivor from the past, sometimes called a living fossil. Scientists think it changed in special ways during its history based on the size of tiny structures on its leaves.

Systematic position

The APG II system (2003) suggests that this plant family can either be grouped with the Proteaceae or kept separate as its own family. When kept separate, it belongs to the order Proteales within a group called eudicots. This is a small change from the APG system from 1998, which did recognize this family. Older systems like the Cronquist system of 1981 placed it in a different order called Hamamelidales. Other systems, such as the Dahlgren system and Thorne system (1992), also recognized this family but placed it in the order Hamamelidales. The Engler system from 1964 put it in the order Rosales, and the Wettstein system from 1935 placed it in Hamamelidales as well. Recent studies using both molecular and physical data show that this family is closely related to the Proteaceae, acting as its version in the Northern Hemisphere.

Taxa included

Main article: Taxonomy

The main group of plants in this family is called Platanus. It was named in 1753 and has a special species called Platanus orientalis. This group is split into two smaller parts. One part includes a special species named Platanus kerrii, which is different from the others and helps scientists understand how these plants evolved.

Hybrids

The London plane or hybrid plane is thought to be a mix between two types of plants, P. occidentalis and P. orientalis. But where it first grew is still a mystery. Some believe it started in London, others think it was in Spain, or maybe even in Turkey. Scientists haven’t used the latest tools to study this, so there is still debate about its name. This special plant isn’t found growing wild, but you can see it near rivers and streams where it has grown on its own.

There is also a hybrid called Platanus × hispanica Mill. ex Münchh., from the year 1770. Other names have been suggested for similar hybrids, like:

• Hybrid Platanus × cantabrigensis A.Henry, from 1919
• Hybrid Platanus × parviloba A.Henry, from 1919

Scientists aren’t sure if the fruit of these plants is called a nucule or an achene. The fruit is dry, doesn’t open when it’s ready, and contains one seed.