Brodiaea santarosae Lecture 2
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Lecture: Santa Rosa Basalt Brodiaea (Brodiaea santarosae)
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PDF of B. santarosae Article Published in Madrono Vol. 54: 187-198 (2007)

Floras Citing Brodiaeas In Southern California
Brodiaea Images: Central & Southern California
  San Marcos Vernal Pools & Brodiaea Populations  

 Blue Background 

This is a new species, not a hybrid between B. filifolia & B. orcuttii

  1. Santa Rosa Basalt: Brodiaea santarosae is endemic to ancient lava flows on the Santa Rosa Plateau known as Santa Rosa Basalt. The flows date back to about 8 - 11 million years ago, to a time before the present mountains of southern California were uplifted. Brodiaea is an old genus that existed in the California region before the climate transitioned to a Mediterranean one without summer rainfall at about 5 million years ago. The corms are adapted to summer drought and periodic brush fires. B. santarosae colonized the basalt flows of the southern Santa Ana Mountains 3 - 8 million years ago. At least 97% of the original basalt has been eroded away. Could this be an old species on the verge of extinction?

      Basalt On The Santa Rosa Plateau  

  2. Hybrid Swarm: Ideally, a hybrid swarm population should have continous variation between the parents. I.e. there should be individuals like B. filifolia with short, filiform staminodes (2 - 3 mm) & short filaments (0 - 1.5 mm), ranging through individuals like B. orcuttii with no staminodes and long filaments (7 - 8 mm). Unlike either parent, B. santarosae has long staminodes up to 7 mm and long filaments up to 8 mm. In addition, the flowers are 40% larger than either parent. Principal Components Analysis of floral parameters indicates that this is NOT a hybrid.

    B. filifolia
    B. orcuttii
    (0 - 1.5 mm)
    (3.5 - 4 mm)
    (7 - 8 mm)
    (2 - 3 mm)
    Very Short
    (1 - 1.5 mm)
    (0.0 mm)

    B. santarosae Not Intermediate Between B. filifolia & B. orcuttii

    Filaments 8 mm; Staminodes 7.0 mm; Flowers 40% Larger

      Images Inconsistent With Hybrid Swarm  
    Floral Variation in Brodiaea santarosae
    B. santarosae & Native Pollinator Bee

  3. Brodiaea filifolia x B. orcuttii: Several individuals of this hybrid have been found growing side-by-side with the parental species in San Marcos. These are fertile, pollen-bearing hybrids with floral characteristics intermediate between the parents. Fertilility is to be expected since the parents have the same polyploid number (2n = 24). Like the parents, the flower size is 40% smaller than B. santarosae. Principal Components Analysis of floral parameters indicates that this is indeed a hybrid.

    A. Brodiaea santarosae has a perianth spread (diameter) of 40 mm. B. Fertile hybrid between Brodiaea orcuttii and B. filifolia has a perianth spread of 28 mm.

      B. filifolia x B. orcuttii Hybrid In San Marcos  
    B. filifolia x B. orcuttii Grown From Corm

  4. Sterile Hybrid: A sterile hybrid between B. filifolia or B. orcuttii and coastal BTK (B. terrestris ssp. kernensis) has also been found in San Marcos. Sterility is expected since the chromosome number of BTK is at least 2n = 36. Although they have multiple sets of the base number of 6, these old species populations apparently behave as diploids (diploidization). Only two sets of maternal and paternal chromosomes associate during synapsis of meiosis, in contrast to quadrivalent tetraploids where four sets of homologous chromosomes associate during meiosis. A hybrid between B. filifolia or B. orcuttii (n = 12) and coastal BTK (n = 18 or higher) would be sterile because the non-homologous maternal & paternal sets of chromosomes that differ in number will not pair correctly during synapsis of prophase I.

    Diploid Hybrid With 2 Sets Of Chromosomes

    AAAAAA & BBBBBB   2n = 12

    Tetraploid With 4 Sets Of Chromosomes:


    Tetraploid At Synapsis: Quadrivalent (Tetravalent):
    (4 sets of homologous chromosomes pair up)

    AAAAAA     BBBBBB     4n = 24
    AAAAAA     BBBBBB         n = 6

    Diploidization: Old Tetraploid Behaves As A Diploid
    Bivalent At Synapsis: 2 Homologous Sets Pair Up
    (2 sets of homologous chromosomes pair up)

    AAAAAABBBBBB     2n = 24
    AAAAAABBBBBB       n = 12

      A Sterile Brodiaea Hybrid In San Marcos  
    Diploidization & Origin Of Sterile Hybrid
    Formation Of Fertile Tetraploid Hybrid
    A Sterile Hybrid: B. santarosae x BTK

  5. Brodiaea orcuttii NOT on the Santa Rosa Plateau: Although a small population B. filifolia occurs near B. santarosae on Mesa de Colorado, B. orcuttii does not even occur on the Santa Rosa Plateau. The latter species primarily occurs in vernal pool areas of coastal San Diego County and Cuyamaca Lake. In a typical hybrid swarm, both parental species occur within the range of the hybrid population.

  6. Potted Corms Of Brodiaea filifolia x B. orcuttii: Morphological and size differences between B. santarosae and B. filifolia x B. orcuttii have been verified in potted corms grown in San Marcos Gabbro.

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