Winged Seeds

Updated: 17/01/15

Cones at Midday, in Summer

After dealing with the mechanism of seed shooting by Leguminosae it will not be difficult to explain the strange sounds heard in forests, woodlands, or boulevards of Pinus halepensis (Aleppo pine) in the hot hours of summer. The pine has plenty of closed cones on its branches (Fig. 3.5.1, photographed in August). The small, green ones (at the upper part of the stem on the right) are half a year old, whereas the large green ones are 1.5 years old and the brown ones are 2 years old. In spring, during days of hot, dry winds, a shattering sound is heard as a result of the scales opening. The scales constituting the cone have fiber of different shrinkage and imbibing qualities arranged in their inner and outer sides. This structure leads to the building up of internal tension when the green cones become brown.

In order to display the opening process I put the cone (from Fig. 3.5.1) near the low flame of my kitchen gas cooker. The scales opened immediately to the status shown in Fig. 3.5.2. Below the large woody scales there are pairs of seeds, each with a wing (Fig. 3.5.3). After remaining for a whole day exposed to the warm solar radiation in Jerusalem, the scales open to a degree that allows the winged seeds to fall from the cone (Fig. 3.5.4). The wing becomes slightly folded into its active aerodynamic shape. This structure induces mobility of the winged seed when falling from the tree as if it were a fan or the propeller of a helicopter. Cone opening takes place in nature during forest-fires.

As children in a neighbourhood rich in pine trees, we took advantage of the easy way to get seeds worth eating, especially during the siege days in Jerusalem. When we tried to open the cones by means of fire or amongst burning embers, this was often rather frustrating: you put the cones into the hot place and wait. When the cones open a momentary flame arises and they are lost. Timing is very important for the survival of the pine-seeds. The natural mechanism is timed so that a quarter of an hour after the fire shock, the cones open and the seeds are ready to be dispersed. By this time the fire that destroyed the crown of the pine is over and seeds escaping from the cone fall on the cold ashes of the forest floor. On rainy days, as in the Silybum and in Phagnalon, the wet cones close, re-opening when dried.

Fig. 3.5.1: Cones of Pinus halepensis. Top right – small ones which started to develop between March and August of this year; the large green ones are 1.5 years old. The left ones are 2.5 years old; the upper one has already opened and spread its seeds.

Fig. 3.5.2: The brown cone which was closed, “smelled” fire from my kitchen cooking stove and started to open.

Fig. 3.5.3: A brown scale, removed in order to expose the wings of the two seeds protected by the scale. Top right – a winged seed.

In this section on pines, a guest from the Papilionaceae is Tipuana tipo (Fig. 3.5.5). It is a common boulevard tree in Israel that produces fruits towards winter. The wing is in fact a seed-less fruit, displaying the typical oblique direction of fibers and veins in the fruit. There are 3-4 seeds in the woody, closed part of the fruit. The aerodynamic structure of the diaspore makes it a sure-fire toy for every parent who wishes to bring his children into direct contact with nature. (I have a small problem – I love the seed dispersal movement, so I try to tell everyone about the Tipuana’s helicopter.)

Fig. 3.5.4: The cone from figure 3.5.2 after being exposed to one warm day in Jerusalem. Each wing is slightly bent, ready to slow down the falling of its seeds by twisting it like a fan or the wings of a helicopter.

Fig. 3.5.5: Fruits of the ornamental tree Tipuana tippo, where most of the legumen is seedless and functions as a wing, forcing the fruit to fall slowly, resembling a descending helicopter. At the base of each fruit there is a seed-containing swelling.