Lambertia formosa, commonly known as mountain devil, is a shrub of the family Proteaceae, endemic to New South Wales, Australia.

It has stiff narrow leaves, and the pink to red flowerheads, made up of seven individual tubular flowers, generally appear in spring and summer.

Although L. formosa is uncommon in cultivation, it is straightforward to grow in soils with good drainage and a partly shaded to sunny aspect.

Specimens of Lambertia formosa were collected by botanists Joseph Banks and Daniel Solander during Lieutenant James Cook's landing at Botany Bay between April and May in 1770.

These are thought to have been obtained from vegetation currently known as the Eastern Suburbs Banksia Scrub that occurs in sandy areas near present-day La Perouse.

[4] French botanist Michel Gandoger described specimens collected at Hornsby and Port Jackson as Lambertia proxima, and material sent to him by plant collector Charles Walter as L. barbata in 1919; these turned out to be L. formosa.

[9] Lambertia formosa grows as a spreading shrub to 2 m (7 ft) tall, with one or more stems arising from a woody base known as a lignotuber.

[13] Lambertia formosa grows in heathland, mallee shrubland and dry sclerophyll forest, predominantly found on sandy or rocky soils.

Here, L. formosa grows under mallee forms of brown stringybark (Eucalyptus capitellata) and broad-leaved white mahogany (E. umbra) and alongside shrubby forms of prickly-leaved paperbark (Melaleuca nodosa), dagger hakea (Hakea teretifolia), scrub she-oak (Allocasuarina distyla), rusty banksia and swathes of kangaroo grass (Themeda triandra).

[14] Lambertia formosa regenerates after bushfire by resprouting from its woody lignotuber, but is also serotinous in that it has a seed bank held in its canopy to be released after fire.

[4] Lambertia formosa is readily grown in cultivation given a sunny position and fair drainage,[8] though it tolerates a range of soils and some shade.

This was a source of nourishment for Australian Aboriginal Peoples and, following European colonisation, explorers, escaped convicts and children were recorded sucking the flowers.

[20][21][22] Explorer Ludwig Leichhardt wrote that "often when I've been tired and thirsty, I've bitten off the base of a tuft of Lambertia formosa flowers to suck the delightfully sweet honey out of them".

[25] First Fleet midshipman and artist George Raper depicted the species in two works: an untitled watercolour study (c. 1788) and Bird Of Point Jackson (1789).