MORELLATO, L.PATRICIA C.* and M.A. PIZO. Departamento de Botanica, Universidade Estadual Paulista, C.P. 199, 13506-900 Rio Claro, SP, Brazil. - A new rain-operated seed dispersal mechanism in Bertolonia mosenii (Melastomataceae), a Neotropical rainforest herb.
Although widespread among fungi, lichens, liverworts, and mosses, seed
dispersal mechanisms operated by rain are unusual among flowering
plants. Generally speaking, two mechanisms are involved in seed
dispersal by rains: splash-cup and springboard. Here we describe a new
seed dispersal mechanism operated by rain in a Neotropical rainforest
herb Bertolonia mosenii Cogniaux (Melastomataceae). The study
was carried out at the lowland Atlantic rainforest, Parque Estadual
Intervales, São Paulo State, Brazil. To evaluate the role of raindrops
dispersing the seeds, 32 plants were assigned to two groups: i)
treatment group were covered with translucent plastic shelters 10-20
cm above the infructescences; ii) control plants were left uncovered.
When fruiting finished, five fruits per plant were harvested and the
seed number was counted. Seed dispersal distances were measured under
laboratory conditions, and the fruit maturation schedule was
monitored. Treatment and control plants differed significantly in the
number of seeds per fruit (mean ± SD = 412.4 ± 186.1 and 52.4 ± 70.7,
respectively; Mann-Whitney tests: U = 269.9, p < 0.001), suggesting
that raindrops represent the mean by which seeds are released from
fruits. The seed dispersal distances ranged from 1.3-29.5 cm (n=97)
and from 1.9-35.3 cm (n=100) when water-drops fall from 1 m and 2 m
height, respectively. Mature fruits were produced during the wettest
months, insuring seed dispersal by rain. We experimentally demonstrate
that rain is necessary to release the seeds from the capsules in an
innovative way we named squirt-corner seed dispersal mechanism: when a
raindrop strikes the mature fruit the falling water forces the seeds
outward to the angles of the triangular capsule through which the
seeds are released. As far as we know squirt-corner represents a new
rain-operated seed dispersal mechanism, and a novel seed dispersal
mode for Melastomataceae, and for flowering plants from Neotropical
forests.
Key words: Atlantic forest, Bertolonia mosenii, hydrochory, Melastomataceae, seed dispersal