The plant diversity of Meiringspoort is one of its main attractions. The species diversity is so high that, for a similar sized area elsewhere in the world, it would be difficult to rival. In 1689, Hendrik Oldenland collected the wild geranium (Pelargonium zonale) that occurs here. Seeds and cuttings were later sent to Europe where the Duchess of Beaufort in England started cultivating them as soon as 1710. They have used this as the basis for the massive geranium industry in Europe and America.

The Swartberg Mountain range divides the Klein and Groot Karoo, and there is a dramatic change in the vegetation from the Klein and Groot Karoo linked by Meiringspoort.

Tree and fern species that is more distinctive of the wetter Knysna forest occur inside the Poort. Mixed amongst these are Klein and Great Karoo plant species, which in turn occur between the typical fynbos plant species.

A large variety of shrub and tree species that are adapted to surviving regular floods grow next to the river in the Poort. This riverine vegetation, such as the Cape Willow (Salix mucronata) and Honey Bell bush (Freylinia lanceolata) have flexible stems and elongated leaves that offer little resistance when submerged during a flood. Their special adaptations enable them to recover soon after a flood. Young trees that occur in and along the river initially also have flexible stems, but later develop a dense root system and strong stems that anchor them firmly.

Three of the plant species growing on the vertical sandstone cliffs are heath species and occur only in Meiringspoort and nowhere else in the world.
They are:
Erica astroites,
Erica umbraticola and
Erica viridiflora.

Erica astroites (refers to its star shaped flowers) only grows along two small water drainage areas in Meiringspoort. It flowers from late August to Mid October. Four other plant species also only occur in Meiringspoort.

Many questions about the plant diversity in Meiringspoort have not yet been answered, such as why the mountain cabbage tree (Cussonia paniculata) occurs only in the northern part of the Poort, while the common cabbage tree (Cussonia spicata) is restricted to the southern half.

It is interesting to note that Meiringspoort is situated in the Swartberg Nature Reserve. The Swartberg Nature Reserve is an Unesco World Heritage Site and starts just after Dam drift and ends before Third toll drift.