Wednesday, January 23, 2013

Variable nascent inflorescence orientation in Arctostaphylos crustacea

Nascent inflorescence deployment is a ecologically interesting feature of manzanitas.  In many species of Arctostaphylos, the inflorescences differentiate and grow in the late summer or fall, only to remain dormant for several months until the onset of flowering in the late winter or spring.

Generally,  characters of the nascent inflorescences are useful in distinguishing some species of manzanitas.  Wells (2000), in his tome “The Manzanitas of California”, recognized Section Nematonascens, consisting of 6 species with erect or gracile nascent inflorescences.  Subsequent phlyllogenetic reconstruction using molecular data (Walhert et al. J. Bot. Res. Inst. Texas 3(2): 673 – 682. 2009) suggests that Section Nematonascens is artificial, or at least that one member Wells attributed to this Section, A. australis of the coast of Baja California within the California Floristic Province, is not related to other Nematonascens (specifically, to A. densiflora or A. stanfordiana).

Arctostaphylos crustacea ssp. crustacea is a common manzanita in central coastal California.  Occasional individuals of A. c. ssp. crustacea exhibit variable inflorescence deployment: some individuals in a population have the nascent inflorescences pendant , while less frequently, rare individuals have erect nascent inflorescences.   In those rare individuals, as the wet season progresses and the flowers begin to differentiate, their stiffly erect nascent inflorescences turn downward and become essentially pendant.

The two photos show nascent inflorescence orientation of a single individual, the top photo taken Dec 11 2012 and the second below taken Jan 21 2013.

Whether or not variable nascent inflorescence reflects a rare, genetically determined heterochrony merits consideration.

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