Biologia floral de uma liana nativa heterodicogâmica, Gouania cornifolia REISSEK (RHAMNACEAE), com potencial para regeneração natural na Amazônia brasileira

Abstract

Gouania cornifolia Reissek (Rhamnaceae) is a shrubby liana native to the Amazon Region, which occurs naturally at forests edges. Its floral biology and pollination are still unknown, despite great ecological potential, since it colonizes areas under harsh conditions (high temperatures and low humidity), and its seeds are wind dispersed, facilitating natural regeneration. This study describes the floral biology of G. cornifolia in natural population in post-mining restoration areas of Companhia Mineradora de Bauxita Hydro, Paragominas, northeast of Pará State, Brazil. Flowering and fruiting periods were monitored monthly during one year. Floral and inflorescence biology were studied in four expeditions with 10- 20 days (June/2019 to September/2019). The floral morphology and floral biology were assessed in 18 plants at least 100 m apart. Tagged flowers were observed from pre-anthesis to full senescence and/or initial fruit development, in order to characterize longevity, floral resources and attractants, petals and sepals positioning, style growth and stigmatic lobes distention. Stigma receptivity was evaluated using the rapid drop hydrogen peroxide test, pollen viability with Baker’s procedure, nectar sugar concentration (% brix) and volume (μl) with hand–held refractometer and icrocapillars, and osmophores with neutral red solution. The flowering period extended from May to mid-September. Fruits began to develop in August, and dispersed seeds in October and November. The inflorescences are terminal racemiform thyrses with small, multi-flowered cymes, and inconspicuous (2 to 3 mm) light yellow-green bisexual and staminate three days long flowers (1:25 sex ratio), opening simultaneously in the same inflorescence. The population showed temporal behavioral floral dimorphisms, comprising two genetic morphs, one with flowers opening around 7:00 am (A07 morph), and other opening around 11:00 am (A11 morph). Bisexual flowers are protandric and in A07 plants sheds pollen in the morning, and the stigma is exposed in the afternoon, conversely, A11 plants sheds pollen in the afternoon and exposes the stigma in the morning of the following day, when it grows, distend the lobes and is reactive to peroxide. At the beginning of anthesis, in both morphs, petals and stamens are perpendicular to the floral receptacle and petals cover the stamens, without, however, preventing the exposure of pollen grains. In A07 and A11 plants, 51 and 68 % bisexual flowers fell within 44 and 82 hours after anthesis, respectively, the rest remained for more than 5 days, possibly developing fruits. Likewise, in A07 and A11 plants, 96 and 88 % staminate flowers fell within 63 and 66 hours, respectively. In flowers with one, two and three days, nectar volume ranged from 0.1 to 1.5 μl with the highest production on the first day, sugar concentration ranged from 50% to 80%, and pollen viability scored > 80%. Osmophores are mainly in the petals and sepals edges, in both morphs. We conclude that G. cornifolia presents a peculiar floral display, with easy access to floral resources, which facilitates entomophily; exhibits sexual dimorphism of the andromonoecious type; protandry-type dichogamy, and a rare reproductive phenomenon, heterodichogamy, the temporal behavioral dimorphisms, where populations of the species comprise two reciprocal genetic morphs.