Abstract

AGUILAR-GASTELUM, Ileem  and  MOLINA-FREANER, Francisco. Flower orientationof two northern populations of Pachycereus pecten-aboriginum (Cactaceae). Bot. sci [online]. 2015, vol.93, n.2, pp.241-247. ISSN 2007-4476.  https://doi.org/10.17129/botsci.232.

Previous studies have documented that flowers of some columnar cacti show equatorial orientation. However, it is unknown how general is this pattern among columnar cacti that produce lateral flowers. Pachycereus pecten-aboriginum is a species that produce lateral flowers and has a wide distribution in Mexico. In this paper we describe the pattern of distribution of flowers across ribs from two northern populations of P. pecten-aboriginum, and explore its relationship with photosynthetic active radiation (PAR) interception. We measured the azimuth and number of reproductive structures of ribs from stems of several plants per population. For one of the populations, we measured PAR for ribs of different orientation and counted the number of ovules per ovary in flowers in eastern, southern, and western positions. Flowers from both populations had a mean orientation of 191.5° ± 69.7° and 194.6° + 61.8°, showing a significant southern orientation. The analysis of the number of ovules per ovary indicated no significant differences among ribs. Daily values of PAR interception showed that southern ribs and the apex received greater values, while northern ribs received the lowest values. Our results are compared with other cacti and we discuss the possible mechanism underlying flower orientation in this species.

Keywords : columnar cacti; flower orientation; Pachycereus; photosynthetic active radiation; Sonora.

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