Discontinued until I can find a non-controversial seed source 

Veronica serpyllifolia

Thyme-leaf Speedwell

• Full sun to partial shade
• Average soils
• 1” tall foliage, 3 to 12” tall blooming stems, 6" to 8” spacing
• Ontario Native, Beginner Friendly, Groundcover
• An 'Underplant' species, these can grow and thrive below and between taller plants, acting as a living mulch

This low-growing perennial is fairly quick to appear after disturbance in a lot of gardens that I’ve worked with in the Ottawa valley, in both sandy, acidic soils and urban, clay-loam. They thrive in full sun, with sufficient moisture, and in partial shade, where they tolerate dryer conditions.

Their low, spreading form is particularly well suited to filling the ecological role of groundcover but they are not as resistant to crushing as many harder stemmed species, so I would recommend introducing them into spaces with infrequent foot traffic, or planting them between stepping stones.  I also think that they are well suited to the role of providing a low growing cover in a strip between taller species and along pathways or roadways where it is important to maintain clear sightlines and avoid any plants that could flop over and impede access for pedestrians or vehicles. 

Their foliage remains very low to the ground, not usually more than 1” in height, and their blooming stems rise to around 3-4” when they are on their own. They can stretch to as much as 12” in height when they are growing among taller species, where they both compete for light and are able to rely on neighbours for a bit of support. They are tolerant of the occasional trimming or mowing and will re-bloom in the summer if the vertical stems are mowed before the tiny seed pods fully mature.

While quick to regenerate from their tiny, dust fine seeds if a site is disturbed, they are not highly competitive when alongside many other perennial groundcovers, such as Lance-Leaved Self-Heal and Wild Strawberries, and will eventually fade away in a mixed groundcover planting.

While some websites indicate that this species was introduced from Europe, VASCAN lists them as native to the majority of Canadian provinces. https://data.canadensys.net/vascan/name/Veronica%20serpyllifolia  

While these tend to be a shorter-lived species in most dense ecosystems, appearing after disturbance opens an area and fading away as the longer-lived species fill back in, they are a helpful species to include when an ecosystem is newly planted since they will quickly cover bare soil. Given their adaptability to sun and shade and a variety of soil conditions, they can be added as a living mulch to almost all new planting areas. The Ecosystem Companions for this Species list below shows species don't require long-term underplanting but that may take a bit of time to completely fill their allocated space and could get along well with a short-term, non competitive neighbour that can keep the soil around them covered for a couple of years.