Transition Studies in Flowering Plants  

by Rolf Baumberger


S03 - Silene 

Another system we are currently investigating is that of Silene dioica - latifolia. We located the system in the Lower Engadine in the east of Switzerland. In 2007 the two forms were interpreted as hybrid forms at 1200 -1400 m of elevation (10.1111/j.1558-5646.2008.00330.x). In contrast to the current situation, where we now assume a transformation process at 1400-1700 m altitude. We will try to support this finding by observation over several years, starting in 2019. Silene dioica has magenta flowers. It occurs in meadows and light woods and is common in early summer. In complete contrast to the white form, which occurs sporadically on a south exposed, well-sunned steep shelves or hedgebanks, and along artificially layered natural stone walls. We suspect that the magenta flowered dioica can transform into the white bloomed latifolia in less than ten years. This system has all the same properties as the Diplacus system also has. We will publish more information on this system here at a later date.  

Silene dioica like plant showing slight attributes of a transition process (base of petioles and stems dark pigmented; white buds turning Lila later on, no real color constancy during anthesis.)

One can observe in the rare instance on the same plant that the color tones of its flowers develops during anthesis from pale Lila to lighter and darker status at the well-developed bloom.


In Val Sinestra at 1640 m of altitude one may see currently (2019) red bloom-ing dioica plants and latifolia like plants that have almost black striped calyces and almost black colored petioles. Hard to interpret this as being the offspring of the hybrid and successive backcross line from the two species. It looks more like a quick transition step, where anthocyanin is pilled up in any plant tissue except the corolla to ensure real white petals. It will be informative to follow the suite of this process. The plant parts should become much less pigmented following the timeline (46.845192 N, 10.35654 E). Such a "contact site" of the two species could not be reported over 1500 m of elevation some 13 years ago in the study of 2006 see: 10.1111/j.1558-5646.2008.00330.x

Silene latifolia a moth-pollinated white flowered species

The transition line 2019 (light blue), in which mixed flower forms are present, lies 2019 200 m (Lavin) to 500 m (Tschlin) above the line 2007 (striped light green). The white-flowered Silene latifolia is becoming increasingly important in the dry, sunny, and steep terrace edges of this landscape, which are very south-facing. As far as the underlying mechanisms are concerned, we are already keeping an eye on them. There should be a logical scientific explanation for this.

Fig: Combined Phase Space

Above additional plot of corolla width in color space; below color plot oft the two Silene morphs and also in-between stages. A1, A2 center oft he morphs stages. Red dashed triangles indicate a linear increase of floral width in mm respectively Light factor. (L=0 means black color; L=100 means white color). From A1 to A2, the two floral traits d & L algorithmically increase gradually. 

The inlet picture shows the potential of a purple flower. Once the petals are white in the early bud stage. The color-forming anthocyanin is only formed during flowering. But what if this were not the case? The flower would remain white - An equivalent to down-regulating of the anthocyanin pathway.

Two cases are distinguished:
Either the two distributions of the two forms do not significantly alter over time, and there are no vegetative changes in the individuals (t >1000 yrs).
Alternatively, one form changes vegetatively via living individuals into the other type (t < 10 yrs) and the transition zone will shift over time. In the first case, the selection theory applies. 

In the second case, the change follows a route --->. One can then determine the temporal course as well as the direction of course. At the latest after five years, it should become clear what exactly is going on. In the second case, a kind of attractor theory seems to describe best. Note that the floral traits d and L show a coupled characteristic according to this phase space (N=520).

Note: Do not overlook the evolutive performance of living systems. Equipped with powerful molecular mechanisms, they can adapt to external conditions within a decade. In this case, the red morph Silene dioica might give rise to the white flowering Silene latifolia. The trigger is undoubtedly a climatic one, which brings more dryness and warmth to the southern flanks of the terrace edges. The formerly red meadow shape jumps into this formation and in a few years turns into the white form that seems to love this niche. At least this is our guess. However, whether this will happen will be confirmed or disproved by observation in the coming years. 

Short Story

r.b. 09-26-19