San Marcos Vernal Pool Area 2012
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San Marcos Vernal Pool Brodiaea Update Spring 2012
  San Marcos Spring 2010       San Marcos Spring 2011      Brodiaea Hybrids In San Marcos 
© W.P. Armstrong 17 May 2012
Note: The Brodiaea, that I referred to as "Coastal BTK," is listed as a possible
undescribed taxon under B. jolonensis in the revised Jepson Manual II (2011)

The following Brodiaea species are flowering in a 40 acre vacant field in San Marcos, CA as of 17 May 2012. Although the heavy clay soil is drying up, there are still a lot of plants in bloom, especially B. orcuttii.
This site comprises approximately 40 acres of vacant land northeast of the William R. Bradley Park and southwest of Palomar College. Like other vernal pool areas in San Diego County, it is composed of undulating topography with clay hardpan depressions and elevated "mima" mounds. Vernal pools are formed as the water from winter rains accumulates in these impervious clay depressions. The vernal pool area is bounded by S. Pacific Street on the west, S. Las Posas Drive on the east, La Mirada Drive on the north, and Linda Vista Drive on the south. This endangered habitat is located within an industrial area and bounded on the east by a large shopping center.

"Coastal BTK" With Purple Staminodes

"Coastal BTK" in San Marcos: The staminodes vary in color from white to purple. Flowers with white staminodes are very similar to plants in Santa Barbara County (Figueroa Mtn and Gaviota Pass). In the Revised Jepson Manual II this species is listed under B. jolonensis as a possible undescribed taxon: "Pls is SW, n Baja CA with green ovaries, white staminodes may be undescribed taxon." Its sporophyte chromosome number is at least 36 compared with 2n=12 for B. jolonensis. Preliminary unpublished research indicates that these two species form closely-related sister clades in phylogenetic trees based on chloroplast DNA.

"Coastal BTK" in San Marcos with white staminodes (photographed in May 2010). Most of the flowers throughout the field had purple staminodes. Flowers with white staminodes are very similar to plants from Santa Barbara County (Figueroa Mtn and Gaviota Pass).

"Coastal BTK" Variant? With Pointed Staminodes

This may be a fertile variant of Coastal BTK with flattened (strap-shaped), pointed staminodes. I have also seen this form at Camp Pendleton and the Santa Rosa Plateau. The only hybrid I have seen between Coastal BTK and B. orcuttii or B. filifolia was sterile with small, undeveloped anthers and no pollen. Another hypothesis is a possible variant of B. filifolia with wider, erect staminodes. Suggestions are welcome.

BTK variant: Corolla unrolled to show pollen-bearing anthers and staminodes (white arrows). The staminodes are flattened and tapering to a point, with small appendages at the base.

  BTK With Pointed Staminodes On Santa Rosa Plateau  
  BTK With Pointed Staminodes At Camp Pendleton  

Coastal BTK x Brodiaea filifolia or Brodiaea orcutii
   A Sterile Hybrid With Flattened (Strap-Shaped) Staminodes
From My 2007 Article On Brodiea Hybrids In San Marcos

This appears to be a hybrid between Coastal BTK and B. filifolia or B. orcuttii which occur nearby. Note the strap-shaped staminodes that are not hooded as in typical Coastal BTK. The flower was completely sterile with no mature pollen grains, giving credibility to the hybrid hypothesis. The clear liquid inside the reduced anther sacs contained cellular debris and scattered nuclei, but no well-formed pollen grains.

This appears to be a hybrid between Coastal BTK and B. filifolia or B. orcuttii which occur nearby. The strap-shaped staminodes are not hooded as in typical Coastal BTK. The flower was completely sterile with no mature pollen grains, giving credibility to the hybrid hypothesis. In his "A Biosystematic Study of the Genus Brodiaea (Amaryllidaceae)", Univ. of Calif. Publications in Botany Vol. 60 (1971), Niehaus reported a cross between B. terrestris and B. coronaria which had a 100 percent seed set. The hybrid progeny of this cross had flowers that were morphologically intermediate between those of the two parents. Pollen fertility of each hybrid offspring was obtained, and the majority were completely sterile. According to Lyman Benson (Plant Taxonomy, The Ronald Press, New York (1962): "If, for example, more than half the pollen grains are abortive, probably something is amiss with the meiotic process preceeding pollen-grain formation." There are several causes for hybrid sterility, including the incompatibility between parental chromosomes during meiosis resulting in failure to pair up properly (nondisjunction) during synapsis of prophase I .

Possible Origin & Of San Marcos Sterile Hybrid

With base numbers of 6 and 8 chromosomes, most species of Brodiaea are technically polyploids with multiple sets of chromosomes. For example, B. terrestris ssp. kernensis in Kern County is an octoploid with eight sets of chromosomes, and B. orcuttii is tetraploid with four sets of chromosomes. [B. jolonensis in Monterey County is diploid with two sets of chromosomes.] According to Niehaus (1971), the lack of quadrivalents in meiosis plus the differences in size of individual mitotic chromosomes at different ploidy levels suggests that these are "old polyploids." That is, the tetraploids, hexaploids, and octoploids have been in existence long enough to change by translocations, deletions, and so on. These differences apparently are enough to ensure that during meiosis only bivalents will occur in the higher ploidy levels. In bivalents, only two sets of maternal and paternal chromosomes associate during synapsis of meiosis, in contrast to quadrivalent where four sets of homologous chromosomes associate during meiosis.

If Brodiaea species behave as diploids, then BF and BO each have n = 12 and 2n = 24, and BTK has n = 18 or a higher number. In fact, BTK could be 2n = 36, 38, 40, 42, 44, 46, 48, etc. and still be theoretically fertile with two sets of homologous chromosomes. A hybrid between BF or BO and BTK would be sterile because of the non-homologous pairs of chromosomes that differ in number. Hybridization may occur, but the resulting hybrid offspring grown from seed may by sterile without viable pollen. For example, a cross between BF and BTK could result in a hybrid with 12 BF chromosomes and 18 BTK chromosomes which would not match up during synapsis of prophase I. This hypothesis is a plausible explanation for the sterile hybrids we have observed in San Marcos.

My tentative chromosome count for Coastal BTK in San Marcos was at least 36. Preliminary chomosome counts of Coastal BTK from Otay Mesa by Dale McNeal at University of the Pacific (personal communication, 2006) indicate that the number may be greater than 40. An exact count is difficult because small chromosomes are often obscured by larger ones.

Microsporogenesis in the San Marcos BTK showing the first division of a pollen mother cell (microsporocyte). Cytoplasmic division (cytokinesis) has not occurred yet. The two chromosome clusters (2 sets of chromosome doublets) contain at least 36 chromosomes, possibly more depending on how you count overlapping chromosomes. There are very small chromosomes that may be obscured by the larger ones. Brodiaea species are known to have base numbers of 6 and 8. [500 x]

Classic Brodiaea orcuttii

Classic Brodiaea filifolia

Brodiaea Grown In Flower Pots In San Marcos

Brodiaea terrestris ssp. terrestris From Coastal Monterey County

Brodiaea santarosae From Santa Rosa Plateau, Riverside County

My 1st Brodiaea santarosae flower in 2012 (28 May).

Brodiaea santarosae in full bloom (7 June 2012).

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