Background:

Research on floral ontogeny in cacti is scarce; this is essential to know the identity of the floral organs and to identify valuable taxonomical characters. In this research the floral development of two species of Echinocereus was analyzed and compared.

Hypothesis:

The development of the floral whorls of the two species of Echinocereus will be in centripetal order.

Study species:

Echinocereus stramineus (Engelm.) F. Seitz, 1870 (Costati section) and E. coccineus Engelm., 1848 (Triglochidiati section).

Study site:

Sierra de Juarez, Ciudad Juarez, Chihuahua, Mexico, year 2019.

Methods:

Buds, floral buds and flowers in anthesis were collected and processed by optical and scanning electron microscopies.

Results:

Eight stages of floral development were established from early organogenesis to anthesis. The floral buds are erumpent. Organogenesis is centripetal in the following order: outer tepals, inner tepals, stamens and carpels. The stamens differentiation is centrifugal, with particularities in each species. The carpels show congenital fusion by developing a unilocular syncarpous gynoecium with parietal placentation. The apical portion of the carpels formed the stigma lobes (8-12). The bifurcation of one of the stigma lobes in both species constantly was observed.

Conclusions:

The bifurcated stigmatic lobe could have taxonomic value, but it should be evaluated in a comparative study that includes other species of Echinocereus. This research allowed us to understand how each floral organ is formed and to detect possible characters with taxonomic importance as for taniniferous epidermis in the tepals and the columnar width.

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