Hi Eve,
Grevillia banksii (Banks' grevillia) and Leptospermum petersonii (lemon scented tea tree) are two that are supposed to perform well in clay soils. I'm sure others will know of more. Good luck,
Dee.

Don't know much about which WA natives tolerate clays, though my hunch would be some of the Melaleucas and your 2 Callistemon spp. -- and what about Grevillea curviloba? -- seems to tolerate heavy soils here in the east.

In western Sydney, where we have a combination of stiff clays and summer spells of very wet and humid weather, 3 favourite local natives of mine grow happily in the clay: the very pretty Melaleuca thymifolia; Eremophila debilis (Myoporum debile); and Grevillea juniperina (type form). These are all attractive shrubs.

Unless you are living in an area of savannah woodland I suspect a good diversity of native shrubs may have occurred on your site pre-clearing. There should be quite a few local natives, especially in your area (which I envy). I live on hard clay loam and have great success with Banksias and Grevilleas, but they're all species from areas with clay. I know quite a lot of the most popular WA plants come from deep sand so would doubtless kark it on clay. My past experience with Eucalyptus caesia (pretty much a shrub where I was in western Sydney at the time) shows it to be tolerant of clay, as is Grevillea biternata.

Other WA species I am familiar with or have heard of taking well to clay include:

Alygone huegelii
Astartea fascicularis
Boronia megastigma (well, maybe touch and go)
Calothamnus quadrifidus
Chorizema cordatum (if given a reasonable humus-rich topsoil)
Eremophila - most seem to tolerate clay around here
Hakea laurina, petiolaris
Melaleuca coccinea (worth a try), diosmifolia, laterita
Solanum aviculare (grows like lightning to about 2.5m)

Some of the eastern natives (and are not too tree-like) that do well on clay in my experience include:

Melaleuca parvistaminea, ericifolia, styphelioides
Kunzea ambigua, parvifolia, ericoides
Banksia marginata, ericifolia, spinulosa, robur, paludosa
Grevillea hyrids of many sorts, aspleniifolia, juniperina
Baeckia virgata
Acacia species (most, especially feathery-leaved ones)
Allocasuarina paludosa
Atriplex nummularia
Bauera rubioides
Callistemon citrinus and cultivars
Calytrix teragona
Correa alba, reflexa cultivars
Crowea all
Dodonaea viscosa
Prostranthera lasianthos, incisa, saxicola
Philotheca myoporoides (used to be Eriostemon myoporoides)
Indigofera australis
Jacksonia scoparia
Leptospermum, lots
Myoporum montanum and various others
Westringia longifolia, fruticosa

Mind you, if you grow on limestone this list may be of sparse use. While most of these species are pretty hardy, some loathe high pH. Also, this list applies mainly to better drained clay (white or yellow to reddish) not soggy stagnant clay (grey). My personal preference would be your own local natives, you have so many real beauties.

You need to obtain indigenous plants from your own area, These will be adapted to the shallow sand and underlying clay. Greening Australia (WA branch) should be able to provide you with a list of indigenous nurseries in WA

What a wonderful response, thank you all so much for your suggestions. I certainly have a good list to choose from

Have you considered your planting technique? Even clay loving plants can die quickly in clay soils if planted incorrectly. Basically, you can drown them as excess water sits in the hole you have dug for them. In your case this ties in with it occurring more where the clay is closer to the surface. Water passes through the sand until it hits the clay surface and rather than continuing it runs along the surface of this layer to the lowest point, including filling the whole you dug for your plant.

Hopefully Greg Boyles from a previous post may reply with his recommendations for planting in clay soils otherwise if pressed I may offer some advice.

Banksia Integrifolia will do well so will B. Spinulosa (try the red form).