Sapindales

The Sapindales are an order of dicotyledonous plants, genetically close to the order Malvales; in the current classifications they include, among the families best known to the Citrus, citrus.

They are characterized by having two whorls of stamens (sometimes one reduced to staminodes), so they are predominantly pentacyclic. Nectar disk of variable position (sometimes reduced to internal glands).

The compound leaves predominate (although in citrus they are simple), the woody habit, the pentameric flowers and the superior ovary. The inflorescences are cymose.

Introduction

Sapindales are disciform superovariate dialipetalous plants, that is, plants with disk-shaped flowers and free petals. They include about 7,000 species. According to L. Emberger (1960), 19 main families belong, with more or less certainty, to this order. The main ones are the Sapindaceae, Anacardiaceae, Rutaceae, Burseraceae, Simaroubaceae and Meliaceae. They are divided into two groups, one close to the Sapindáceas and another to the Rutáceas. Thus, this order was once two, or even three, orders: the Rutales, the Sapindales, and the Terebinthales.

The general characteristics of the Sapindales are their tropical or subtropical location, the woody nature of the vegetative apparatus, the presence of a developed internal secretory apparatus and a simplification of the floral plan from a basic pentameric formula. This group is economically important as it contains, among other things, wood for joinery, particularly mahogany, essential plants used in perfumery, and the huge citrus group (Rutaceae).

The ex-Rutales comprise 5 main families that are recognized by the characteristics of their secretory apparatus: the Meliaceae have isolated secretory cells, the Rutaceae have globular sacs, the Simaroubaceae have elongated perimedullary secretory tubes, these tubes are found in the bast in the Burseraceae and the Anacardiaceae, these two families are distinguished by their ovules, which are epitropic and pendulous in the former, and apotropic and erect in the latter.

Neighbours of the ex-Rutales, the Sapindales in a restricted sense have flowers that are often zygomorphic, unisexual, pentameric or tetrameric. The corolla is present at first, but the apetalia becomes more pronounced. The androecium undergoes reductions while it tends to perigyny. The disc is frequently extrastaminal. The two- or three-fold ovary contains one or two apotropaic ovules. The fruits are vesicular or winged. The exalbuminous seeds are usually surrounded by an aril generated by the funicle. The leaves are usually pinnately compound. The main families are the Aceraceae, whose fruit is a disamare, the Hippocastanaceae with a loculicidal capsule and the Sapindaceae with arilated seeds; the Sabiaceae, Julianaceae and Melianthaceae are of little importance.

This group constitutes a natural block that, according to A. Takhtajan, derives from the Saxifragales. It has affinities with the Geraniales through the Androecium obdiplostemonium and the identical basic floral formula: 5S + 5P + 5E + 5E' + 2-5 C, mainly through the Rutaceae, which differ only in the presence of a well-organized hypogynous intrastaminal disc, the presence of a secretory apparatus, and the fact that these plants are woody rather than herbaceous. The status of some families, which are sometimes placed in one order and sometimes in another, remains unclear. There are also links with the Euphorbiales, and the same problem arises with the Buxaceae, whose belonging to one order or another has been discussed by some and approved by others. From these considerations it can be deduced that, for certain marginal families or less, there are multiple links with other orders. Evolutionary trends are observed towards the Celastrals, Rhamnales, for example. L. Emberger sees a relationship with the Apiales and the Rubiales; he places this group, including the Anacardiaceae, in the same phylum.

Fossil remains have been found in temperate and cold regions of the Cretaceous and Tertiary periods, where deciduous vegetation abounded, especially rich in aceraceae. In the lower Eocene of North America and England, Rutaceae, Anacardiaceae and Sapindaceae have been collected, some of whose representatives have survived to the present day.

Families

This order contains nine families, about 460 genera, and about 5,700 species. More than half of the species of this order belong to two of its families: Sapindaceae (with about 1600 species), where both Hippocastanaceae and Aceraceae are found; and Rutaceae (with about 1,800 species).

• Sapindaceae (about 1600 species)
• Nitrariaceae
• Rutaceae (about 1800 species)
• Meliaceae (about 621 species)
• Simaroubaceae (about 95 species)
• Anacardiaceae (about 600 species)
• Burseraceae (about 550 species)
• Kirkiaceae
• Biebersteiniaceae

The three families in which the number of species is not detailed, add up to 27 species between the three.