Beware: except genetics, color of some flower petals are also affected by epigenetics. Environment factors such as temperature make color change. One example is the Black roses (see picture). [but, I am not sure for Rubus]

Below is one paragraph from WikiHow ( http://www.wikihow.com/Grow-Black-Roses ): How to grow Black roses. They include some research papers. You can read them for further information.

5. Experiment with temperature as the buds grow larger. During this stage, temperature can drastically affect color. Most rose varieties have not been researched in this way, so you'll have to be a pioneer. If possible, try different techniques on different buds or bud clusters. Here are some guidelines to get you started: Cool temperatures tend to increase the amount of pigment produced, which usually means darker flowers. One study of Crimson Glory roses produced purplish roses at 73ºF (23ºC), and darker, redder roses at 50ºF (13ºC) [6]. This is more likely to work in summer [7]. Heat stress usually leads to faded or more orange flowers, but there are exceptions. For example, Baccara roses may end up deepening to a bluer shade [8]. This is a risky technique that can cause flower or plant death; if possible, ask a florist to help you choose temperatures that will stress the plant without killing it. One study of (orange-colored) Jaguar roses exposed buds to three days of 102ºF (39ºC) daytime / 64ºF (18ºC) nighttime temperatures [9].

I think the pink colour of the petals is genetically fixed. The pink colour often fades in sunlight as a result of which the petals seem white in later stage.

Beware: except genetics, color of some flower petals are also affected by epigenetics. Environment factors such as temperature make color change. One example is the Black roses (see picture). [but, I am not sure for Rubus]

Below is one paragraph from WikiHow ( http://www.wikihow.com/Grow-Black-Roses ): How to grow Black roses. They include some research papers. You can read them for further information.

5. Experiment with temperature as the buds grow larger. During this stage, temperature can drastically affect color. Most rose varieties have not been researched in this way, so you'll have to be a pioneer. If possible, try different techniques on different buds or bud clusters. Here are some guidelines to get you started: Cool temperatures tend to increase the amount of pigment produced, which usually means darker flowers. One study of Crimson Glory roses produced purplish roses at 73ºF (23ºC), and darker, redder roses at 50ºF (13ºC) [6]. This is more likely to work in summer [7]. Heat stress usually leads to faded or more orange flowers, but there are exceptions. For example, Baccara roses may end up deepening to a bluer shade [8]. This is a risky technique that can cause flower or plant death; if possible, ask a florist to help you choose temperatures that will stress the plant without killing it. One study of (orange-colored) Jaguar roses exposed buds to three days of 102ºF (39ºC) daytime / 64ºF (18ºC) nighttime temperatures [9].

Dear Boroka,

If you like, you can contact Chandani Gupta

She is revising the Indian species of Rubus.

With best wishes,

Subir.

Thank you very much Arvind, Yuan-Yeu and Subir for your replies!

All identification keys include petal colour (white versus pink) and I was wondering whether it is a good character to use or as you mentioned, it might be just phenotypic plasticity induced by the environment. 

Thank you again, I will be in touch with Chandani Gupta.

I have revised the Indian members of Bauhinia and allied genera. The colour of the flowers might not always have good taxonomic value.

Hello,

Flower color could be influenced by abiotic factors, as discussed above temperature is one of them, pH is one of the main players. In case of Hydrangea plants, acidic soil change flower color to blue, while in alkaline it's pink, and pH=7 is purple.

another example is in Ipomea tricolor flower, if wild type with a determined blue color flower, and then you examine the flower bud 12 hours before bloom, the petal color is actually purple and changes to blue upon blooming.

In case of Rubus as far as I have seen color range between white and pink, if you want to further examine petal color you can look in the pink color intensity in petals, is it pale pink or solid pink color? which could be due quantitative genetics influence, agronomic practices, or abiotic factors.

Thank you both - indeed, I would like to discuss that petal color is more due to abiotic factors and might not have good enough taxonomic value. 

I am also revisiting leaf and prickle morphology - since Rubus taxonomy is mostly based on morphological characters, I would like to find out how abiotic and biotic (competition, herbivory) influence these characters. 

@ Boroka Kiss,

1. The attached paper is an excellent source in discussing 'flower color and development'.

2. In the paper, it also mentioned that 'Light Intensity' is another important factor for plant flower color change (see below). That means that for some plant species, the flower color could be different when you sample them on noon or at evening.

"Light is another major factor that affects flower color, particularly light intensity, light quality and photoperiod. Based on their requirements for light intensity, plants are classified into heliophytes and sciophytes, and they can only grow well under appropriate light intensities. For example, as a heliophyte, flowers of tuberose are purplish red under strong light intensities, but their color fades under weak light intensities (Huang et al., 2000). This effect also occurs in boronia (KangMo et al., 2007). Shade is a commonly used gardening method for the modification of light exposure. Huang et al. (2000) found that the tuberose flowers cultivated at 25∘C were almost white by 45% shading, but pale reddish-purple under 25 or 0% shade treatment, which was related to the enzyme activity participating the biosynthesis of anthocyanins. Meanwhile, in herbaceous peony, 60% shade caused significantly reduced anthocyanin content and lighter flower color (Figure Figure55), mediated by the synergistic action of structural genes involved in anthocyanin biosynthesis and especially the downregulated expression of PlPAL, PlCHS, PlF3H, and PlF3′H (Zhao et al., 2012a)."

You should include some molecular data to support morphological character data for your Rubus phylogeny study.

Thank you Yuan-Yeu - it is a great paper! 

I am planning on collecting fresh material as well but former papers tent to point out how hard it is to find the right markers because of the different ploidies. So I would like to focus on morphology and their phenotypic plasticity. 

This is 'just and undergraduate project' but I think gene expression of Rubus in different environments would also be a very interesting to research - might prove to be crucial when considering their taxonomy.