There are 239 species of indigenous vascular plant recorded from the LHIG, of which 113 (47%) are endemic. The high degree of endemism is illustrated not only at the species level, but also at the generic level, where there are five endemic vascular plant genera (Negria, Lordhowea, Howea, Lepidorrhachis and Hedyscepe) (Hunter 2002).

The non-vascular flora of terrestrial and freshwater habitats (bryophytes, lichens and freshwater algae) is less well known, but is also considered to be diverse with many endemic species. For example, 105 species of mosses are known, 21 (20%) of which are endemic (Ramsay 1984). 

New species of endemic vascular and non-vascular plants from the LHIG continue to be described. Approximately 271 species of vascular flora have naturalised (introduced species that are reproducing in the wild) on the LHIG since settlement. Some of these, including Bitou Bush (Chrysanthemoides monilifera), Ground Asparagus (Asparagus aethiopicus), Climbing Asparagus (Asparagus plumosus), Bridal Creeper (Asparagus asparagoides), Cherry Guava (Psidium cattleianum), Sweet Pittosporum (Pittosporum undulatum), Kikuyu Grass (Pennisetum clandestinum), Crofton Weed (Ageratina adenophora) and Tiger Lily (Lilium formosanum), pose serious problems as environmental weeds, and 18 species are declared noxious for the LHIG.

Over 70 species of plants on LHI are impacted by rodents.

The below list shows listed threatened plant species on Lord Howe Island currently impacted by rodents:

Little Mountain Palm

Lepidorrhachis mooreana

A stout, dwarf palm with a trunk to 2m high.
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Phillip Island Wheat Grass

Elymus multiflorus var. kingianus

Phillip Island Wheat Grass is a tufted perennial grass, 30–100 cm tall, with a low, spreading habit and narrow glaucous leaves 3–5 mm wide.