Themidaceae

[Robert]

> Triteleia laxa  El Dorado County, California

The Brodiaea Family, Themidaceae, is a diverse group of bulbous perennial corms found from Central America through Western North America. The University of California currently recognizes 7 Genera and 45 species native to California. This includes a large number of endemic species.

In California, the Themidaceae are a highly adapted group found within almost every floristic province within the state. Most have evolved to a Mediterranean type climate where the corms become active with cooler temperatures and the commencement of precipitation in the autumn. During the spring months they grow rapidly and produce flowers from March through June depending on location and the species. During the hot, dry summer months the corms go into dormancy and spend the summer resting until the cooler autumn temperatures and precipitation begin the growth cycle again. An exception to this pattern are some of the high elevation, mountainous species which break dormancy in the spring with snow melt and continue with active growth into the summer before going into dormancy late in the summer season.

In this thread I will limit my discussion, for the most part, to 4 Genera: Brodiaea, Dichelostemma, Dipterostemon, and Triteleia. The discussion will be based on my extensive field studies of these plants primarily in El Dorado County, California, as well as my field studies throughout Northern and Central California. At times I will include comments concerning my ongoing breeding work with these species.

My hope is that others will share their experiences with the “Brodiaea’s” so that we can all benefit from the information. The Themidaceae are likely adaptable to a larger range of climatic/horticultural situations and applications than are currently in use today. We just need to experiment and trial these plants over a broad range of environmental conditions to gain a better understanding of their capabilities as ornamental plants.


Triteleia ixioides ssp. scabra  El Dorado County, California

[Robert]

In the lower foothills of the Sierra Nevada Mountains of Northern California, the corms of many Themidaceae species break their summer dormancy during the autumn, with the commencement of lower temperatures and the beginning of the winter precipitation season. Pictured above, is the new growth of Dipterostemon capitatus ssp. capitatus as photographed on 21 December 2016 at our El Dorado County farm situated at an elevation of 1,500 feet (457 meters). Abundant precipitation fell in our region during October and November of 2016. This facilitated rapid and lush new growth. During seasons of drought new growth can be less abundant, however the corms generally break dormancy during this same time period.

In Themidaceae, the gene expression of anthocyanins in the new growth is regulated by transcription factors that respond to environmental variables, in this case in particular, temperatures. In general the cooler the temperature, the greater the expression of purplish pigmentation in the new growth. This purplish pigmentation can be quite attractive and can be a valuable horticultural characteristic.



Pictured above are hybrid seedlings of Dipterostemon capitatus ssp. capitatus coming into growth this autumn in our Sacramento garden. Selection for enhanced purplish pigmentation of the new growth is being made with this group of seedlings.  Solar radiation can also influence the expression of anthocyanins in the new growth; thus careful observation is necessary when selecting the best plants to grow seedlings on to the next generation.



Dichelostemma multiflorum is generally found at higher elevations in our region. Pictured is Dichelostemma multiflorum growing with Viola purpurea ssp. integrifolia on Peavine Ridge in El Dorado County, California, at an elevation of 5,125 feet (1,562 meters). At this site, the expression of purple pigmentation in the new foliage of Dichelostamma multiflorum can be intense. Such plants are extremely desirable and are well worth cultivating in the garden. The purplish pigmentation contrasts well with plants with yellow foliage or flowers.



Pictured above are Dichelostemma multiflorum seedlings growing in our Sacramento garden derived from plants with deep purplish foliage on Peavine Ridge. There is considerable variation in the expression of purplish anthocyanins among these seedlings. Solar radiation is certainly a factor involved in this gene expression, however a small percentage of the seedlings continue to express purplish pigmentation in the foliage, even with higher wintertime daily high temperatures and frequent periods with low levels of solar radiation. This is an on going project where further enhancement of the purplish foliage characteristic is a primary goal.

Another desirable characteristic arose from this group of seedlings: A small percentage of the seedlings have distinctive pinkish-purple flowers, very different from the much more common lavender colored flowers of this species. This flower characteristic will also be pursued.

Purplish-pigmented foliage adds a new dimension to a number of Themidaceae species at a time of year when there are few flowers in bloom in the garden. I am continually amazed at the genetic variability of plant species.