What is the Matrix?

Landscape Architect Thomas Rainer, in his blog post How to Create a Planting Module, discusses a different approach to configuring your planting design.

1-2 matrix species:  clump forming grasses and some perennials
2-5 cluster species: slowly spreading rhizomatous or stoloniferous species
1-2 structural species / visual anchors trees: large shrubs, certain perennials

If I were to design a module using these natives (below), what is the matrix? The only grass appears to be the inconspicuous Mountain brome (Bromus marginatus). The matrix might likely be the dominant shrub species.  What is the structure species? These are wide-open meadows. Is it the Douglas fir on slopes at the margins?

Two places above 9,000 feet.

One: north-west facing, morning shade, mid-day/afternoon sun.

Mountain snowberry matrix

The other: south-facing, full sun, very late afternoon shade (pretty much full sun) about 200 feet higher in elevation than One.

Artemesia matrix

The cluster plants are similar in each place but the shrubs are different.  One is Mountain snowberry (Symphoricarpus oreophilus), the other is a species of sagebrush (Artemesia spp).

Clusters include lupine, larkspur, asters, paintbrush, little leaf (?) sunflower, Giant Nettleleaf hyssop (Agastache urticifolia), clematis, at least three species of Penstemon.

I am no expert on native plants but I love to see how they grow together in associations.  The explosion of color and texture delights the eye. Bees and hummingbirds are a constant sound throughout.

So, let the matrix be a low shrub species.