I have a feeling that the white one is Lobularia maritima and the others belong to Alyssum? Could anyone differentiate between Lobularia and alyssum with these images?
Lobularia maritima is the binomial (that is, scientific name) for the annual, "sweet alyssum". If you click on the following link, you'll see the various flower colours for Lobularia maritima:
Do your plants have some particular characteristics that differ from Lobularia maritima?
Note that flower colour is not necessarily a distinguishing characteristic, particularly for species that have been in cultivation a long time. (I assume your question largely arises from the different flower colours you have among what appears to the same species, from what can be seen in your photos?)
This message was edited Nov 24, 2012 9:39 PM
these images are taken about 3 years ago. i heard something like "sweet alyssum" but the true genus is probably Lobularia. I think you are right that the flower colors are not an essential distinguishing characteristic.
So we settle these images are Lobularia? I am leaning that way.
There are several cultivars of L. maritima that are some shade of pink, so I definitely wouldn't rule it out based on color. http://davesgarden.com/guides/pf/adv_search.php?searcher%5Bcommon%5D=&searcher%5Bfamily%5D=&searcher%5Bgenus%5D=lobularia&searcher%5Bspecies%5D=&searcher%5Bcultivar%5D=&searcher%5Bhybridizer%5D=&searcher%5Bgrex%5D=&search_prefs%5Bblank_cultivar%5D=&search_prefs%5Bsort_by%5D=rating&images_prefs=both&Search=Search (note--given variations in how colors appear depending on cameras/lighting I wouldn't necessarily try to figure out which exact variety you have--I don't think you can ever be certain. I just posted the link to show that there are plenty of pink ones)
In addition to habit annual (Lobularia) or Perennial ((Alyssum), what can really help in identification is that plants of Lobularia maritima are usually shorter than 15 cm whereas they are almost always taller than 15 cm in Alyssum.
I recall these plants are pretty low, almost hugging the ground. I think Singhg45 is correct that L. maritima plants are shorter than Alyssum.