Brodiaea santarosae
The Santa Rosa Basalt Brodiaea

Tom Chester, Wayne Armstrong and Kay Madore

Distinguishing Characteristics of Brodiaea santarosae: Habitat, Peduncles, Bracts and Pedicels

Habitat. The habitats of the four species are distinct. B. filifolia and B. orcuttii are confined to the wettest areas such as flat streambeds, benches along streambeds, and vernal pool areas. B. terrestris ssp. kernensis and B. santarosae are less moisture-dependent. B. terrestris ssp. kernensis grows in many habitats, but generally does not occur in the wettest areas preferred by B. filifolia and B. orcuttii. It grows in drier drainages and along trails and roads in flattish areas.

Brodiaea santarosae grows in many habitats as well, including next to vernal pools, but can grow in drier locations than even B. terrestris ssp. kernensis. Surprisingly, B. santarosae even grows in disturbed areas such as Waterline Road next to the Mesa de Burro. That area was completely dug up to install a water main, and B. santarosae grows abundantly in the disturbed soil on top of the water pipe, as well as in roadside berms.

There is only one known occurrence of B. filifolia within the range of B. santarosae, on the Mesa de Colorado immediately surrounding the largest vernal pool. The area in which it grows was part of that pool for ~75 years, when the outlet of the pool was dammed to raise the level of the pool. The soil in that area is heavily leached, and does not have the red color of the surrounding basalt-derived soil. B. santarosae is not found on that vernal pool soil, only in the red basalt soil elsewhere on the Mesa de Colorado.

Of course, the most remarkable difference in habitat is the restriction of B. santarosae to basalt soil in areas on or near the Santa Rosa Basalt.

Fig. 4A. Histogram of peduncle lengths for B. filifolia (B.f.), B. orcuttii (B.o.), B. santarosae (B.s.), and Mu ssp. kernensis (B.t.k.). Zoomable PDF version.

Peduncle and bract lengths. Histograms of these two parameters (Figs. 4A and 4B) each showed two distinct patterns: B. filifolia and B. orcuttii had similar histograms that peak at shorter values, and B. santarosae and B. terrestris ssp. kernensis had similar histograms that peak at longer values. For example, 60% of the peduncles for B. filifolia and B. orcuttii were less than 150 mm, but only 27% of the peduncles for the other two species were that short. Even more dramatically, 65% of the bract lengths for B. filifolia and B. orcuttii were less than 6 mm, but none of the bract lengths for the other two species were that short.

Fig. 4B. Histogram of bract lengths for B. filifolia (B.f.), B. orcuttii (B.o.), B. santarosae (B.s.), and Mu ssp. kernensis (B.t.k.). Zoomable PDF version.

Although it is possible that the peduncle length further distinguishes B. santarosae from B. filifolia and B. orcuttii, we suspect the peduncle length is subject to environmental modification by the height of the immediately-neighboring plants, which in turn derives from the different habitats of these species. Peduncles are shorter where there are few neighboring plants, and longer where the plant is surrounded by tall annual non-native grasses. Both B. filifolia and B. orcuttii are found in habitats that largely exclude non-native annual grasses, whereas B. terrestris ssp. kernensis and especially B. santarosae are found in drier habitats that favor those grasses. Supporting our suspicion, the range of peduncles is essentially the same for every species even though the histograms are different, implying that each species grows its peduncle long enough for its flowers to be out in the open.

The difference in bracts is more fundamental since the range for bract lengths is very different among the species; there seems to be a firm upper limit for the bract length of B. filifolia and B. orcuttii.

Pedicel lengths. As for the peduncle and bract lengths, B. filifolia and B. orcuttii had a similar pattern with histograms that peak at shorter values (Fig. 4C). However, B. terrestris ssp. kernensis had a histogram shifted only slightly to larger values, where B. santarosae had a histogram shifted dramatically to larger values. For example, all pedicels of B. filifolia and B. orcuttii were less than 60 mm, but 37% of the pedicels of B. santarosae, and 13% of the pedicels of B. terrestris ssp. kernensis, were greater than 60 mm.

Fig. 4C. Histogram of pedicel lengths for B. filifolia (B.f.), B. orcuttii (B.o.), B. santarosae (B.s.), and Mu ssp. kernensis (B.t.k.). Zoomable PDF version.


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Copyright © 2007 by Tom Chester, Wayne Armstrong and Kay Madore.
http://tchester.org/plants/analysis/brodiaea/bsr/habitat.html
Comments and feedback: Tom Chester
Last update: 16 October 2007