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Themidaceae: Brodiaea terrestris ssp. kernensis
Themidaceae: Brodiaea santarosae
Themidaceae: Brodiaea terrestris ssp. kernensis x B. santarosae
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This small brodiaea population on Mesa de Colorado appears to be sterile hybrids between B. terrestris ssp. kernensis (BTK) and Brodiaea santarosae which grow intermixed in certain areas of the Santa Rosa Plateau. The large, strap-shaped staminodes resemble BTK; however, the slender, apical extensions resemble Brodiaea santarosae. Another possible parent is B. filifolia; however, the staminodes of the later species are threadlike (filiform). The anther sacs of these putative hybrids generally are devoid of pollen, with only cellular debris and some malformed pollen grains. The hybrids undoubtedly represent a clonal population that has reproduced asexually from cormlets. The best hypothesis to explain the pollen sterility is non-homologous parental chromosomes resulting in synaptic failure during microsporogenesis. The most likely parental species (BTK and B. santarosae) have different chromosome numbers. The dissimilar maternal and paternal chromosome sets in the hybrid fail to pair up properly during synapsis of Meosis I. Numerous flowers in this population were carefully examined during a period of three years, and they were all sterile. The presence of viable pollen in one flower sample from this location is unexplained at this time.
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The above anthers are undersized and devoid of mature pollen grains. This is to be expected in hybrids between parents with different chromosome numbers, such as BTK and B. santarosae. Tentative chromosome counts by this author for coastal BTK in San Marcos are at least 36. Tentative chromosome counts by Dale McNeal of University of the Pacific for coastal BTK on Otay Mesa appear to be greater than 40. Niehaus (1971) gives chromosome counts of 48 for BTK in Kern County. His number of 36 for B. jolonensis on Otay Mesa is undoubtedly from coastal BTK. The diploid number for B. santarosae is not known precisely at this time, but tentative counts by Annette Winner of the San Diego Natural History Museum indicate that it is in the low 20s. My observations of microspore mother cells of B. santarosae indicate a chromosome number much lower than BTK. According to Niehaus (1971), the diploid chromosome numbers of B. filifolia and B. orcuttii are 24. Based on similar floral morphology, the chromosome number for B. santarosae is probably closer to the latter two species. Visible pollen grains on the perianth segments in the above images undoubtedly came from insects, including small beetles and flower bees, or possibly by the wind. The following image reveals the presence of one pollen-bearing flower within this small hybrid population. The staminodes appeared identical to those of the adjacent sterile hybrid flowers.
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The following image shows pollen from a fertile flower within the hybrid population.
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Pollen from one flower collected in the hybrid population. Of all the many dozens of flowers examined from this location, this is the only one with viable pollen. Its presence among all the sterile flowers is an enigma at this time. Stained with acetocarmine. 100x magnification.
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The mule is a classic example of a sterile hybrid with non-homologous parental chromosomes that fail to pair up properly during synapsis of Meiosis I. A mule has an odd chromosome number of 63. It received 31 chromosomes from the sperm of its donkey father (jackass) and 32 chromosomes from it horse mother (mare). Although rare, there are documented records of a female mule giving birth to a foal. Oogenesis (meiosis inside the ovaries) apparently did not go awry and actually produced a viable egg. In the case of sterile brodiaea hybrids, apparently microsporogenesis (meiosis inside the anther) sometimes results in fertile pollen.
Euphorbiaceae: Chamaesyce albomarginata
Mesa de Burro
Campanulaceae: Downingia bella
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What appears to be sparkling blue water in these next three images is actually a dense population of Downingia bella (Campanulaceae) growing in the damp soil of a large, desiccated vernal pool.
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Poaceae: Orcuttia californica (California Orcutt Grass)
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The light green border surrounding the dense, blue population of Downingia bella is California Orcutt grass (Orcuttia californica). This is a rare annual grass endemic to vernal pool habitats in southern California.
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Poaceae: Orcuttia californica and Alopecurus saccatus (Foxtail Grass)
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Two native annual grasses at Mesa de Burro. A. California Orcutt grass (Orcuttia california). B. Foxtail grass (Alopecurus saccatus).
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Polemoniaceae: Navarrettia intertexta
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