Transitions Studies in Flowering Plants: Real-time Evolution   

by Rolf Baumberger

Results so far: Results of Long Term Study in Diplacus 1995 ... 2022 


Fig. 1: (A-G). Phenotypic Transition in Populations

The figure represents the dynamic floral color transitions in red, mixed, and yellow populations between 1996 and 2016. Mixed plant populations were previously assigned to the hybrid origin, while the present study states that the transition stages are the consequences of a dynamic progression of individual plants beginning with the yellow flower morph and consistently ending with the red flower form. The red morph D. puniceus has also become dominant in the east and north, while the former hill and mountain morph of the yellow-flowered D. australis is today restricted to the central southern and northern edges of the San Diego district. The border extends at speed between 300 and 800 m per year (arrows) — the map based on the monitoring of 70 populations over 20 years. Inlets show the corresponding flower shapes.

Red circles: pure red-flowered D. puniceus populations of the morph type in Fig.1G; yellow circles: pure yellow populations of D. australis populations of the morph type in Fig.1; 1B; orange circles: Populations in transition with morph types in Fig.1 C to E; dotted line: yellow border 1962; bold dotted line: yellow border 1996; dotted line: yellow border 2016; B1 ... B6: Locations along a 60 km long transect.

Fig. 2:


Twenty plants within the transition zone were monitored once each year in San Diego and Riverside Counties between 1996 and 2015. Two stable plants from Campo (Y) and Point Loma (R) from the extreme ends of their occurrence served as references. Eighteen plants (2-19) within the transition zones show the individual ascent and descent of the color transition of their color values more or less progressively towards orange and red tones. The two stable plants (Y and R) showed no color transition tendencies.


Two transition plants, T27 and T30, have been monitored since 2002 in Ballena Valley, San Diego County, CA. In the field, the flower color steadily progressed from light yellow-orange (A, C) to red (B, D, E). Cuttings of the year 2009 of these two plants monitored for six years in a greenhouse in Zurich had stable color shades.


Plants 1-2 and 5-10 monitored at Rainbow site.

Fig. 3: (A-B). Heritability- reversion from two different origins

The figure shows a comparison of plots of crossed red-flowered siblings (R3xR7 = Rc) from plants sampled at the coast against red-flowered siblings tested 15 km inland (R14xR15 = Ri). The inland results show significantly more variation and demonstrate more extreme values compared to the coast values. The reversion quote from red to yellow state is between 1.2 and 4.8 % see* that lies well outside of the ±2SD range. In Fig.1, Rc and Ri are plotted on the map together with the transect.


Fig. 4: Floral Color Monitoring in Rainbow & Rancho Populations


Monitors two transient populations by sampling every five to eight years. Sample selection was repeated in two populations with more than 250 individuals geographically spaced 15 km apart, both in unmarked and in different plant individuals.


The color distribution in 2001 for Rainbow and 1997 for Rancho was broad and inclined to the yellow side. After that, the median color shifted permanently to 9.0. The variance (S 2) is lowest at the last census, missing yellow hues that were so obvious 15-20 years ago. The result at both sites is a very similar floral color transition dynamics in populations within the transition zone. The censuses of both populations do not differ significantly (p=0.18) in 2016; they converge to the same final state of more or less uniform red morphs.



Fig. 5: (A-B). Age Structure at Rancho population

(A) The figure shows the age structure in a typical population of over 250 plants of the softwood shrub Diplacus aurantiacus situated at Rancho California Rd. The study used a sample survey along a 60 m long transect line with a maximum of 1 m lateral deviation.

The age structure is based on the number of tree-rings (N=32). It can be deduced that the average lifespan of Diplacus is 31 years, a possible lifetime of 10 to 70 years.


(B) Depicts cross-section of a 23-year-old shoot; one can see more or less pronounced tree-rings. 

Fig. 6: (A-F). Correlation of the distance to the coast versus six different floral traits

Clinal variation of some flower features is depicted. A nearly linear correlation, which is supported by the regression lines, is decreasingly seen on the one hand length of the corolla length (A) and the other hand by the corollary width (B) heading from inland to the coast.

For additional floral features such as pedicel length (C), floral angle (D), style length (E), and Methuen flower color (F), the linear correlation shows an increasing positive level heading from inland to the coast.

The mean color values are rising steeply in the populations but then remain constant MCU 9, red. «H» indicates the «transition zone» with showy, differently colored flowers in populations. This zone «H» has until now been interpreted as a hybrid zone.


Fig. 7: Inheritance at the individual level of two plants in transition


In a greenhouse experiment, the color morphs of two individuals in transition were tracked using inbred lines of cuttings harvested in the field. The cuttings of these individuals were taken twice from plants in Ballena Canyon (San Diego County) within 14 years.

The development of the individual cutting patterns was followed separately (see above the different shades). The overall broadly colored flower color variation of both progeny lines developed significantly towards redder shades during the observation period.