@ Plant phenotype is the appearance of plant species. It described the morphological features of the plant. On the basis of phenotypic characters, one can identify species. Plants with same genetic make up are suppose to have the same phenotype. But variation occurs due to environmental factors. Sometimes the species with different genetic background may have the same phenotype. And these species are known as 'Phenocopies'.  The same species with different phenotypic traits are known as morphotypes. These morphotypes may have some variation at the chromosome level. If so these are known as cytotypes. Otherwise P=G+E. The Phenotype(P) or appearance of a particular species depends upon the genes(G) and prevailing environmental(E) conditions. Phenotype is of utmost important in taxonomic studies. Also the correct identification of the species is highly required to use it for different purposes. Therefore, phenotype has its own significance in life sciences. 

Plant phenotypes are to be essentially studied in the field.  Morphological traits vary for the same species in different habiats. For example, Suaeda maritima and S. monoica exhibit different growth and seed traits in high and low salt marshes as adaptations to such habitats.  Morphological traits are configured by local ecological conditions.

The "field" is the most important. "Lab" and "greenhouse" may be a valuable help in confirming a diagnosis and facilitating the understanding of possible relationships between species and genera. 

Plant phenotyping describes mainly the exterior appearence of plants, regarding differences between species, cultivars, but also the effect of transgenesis or specific treatments on a particular aspect of a plant´s morfological aspect.

One can describe variations in leaf venation or serration, spatial patterning of floral buds or changes in leaves arrangement around the stem or the center of the rosette, depending on the tissue analysed and the particular morphology of the species under study, amongst others.

It can also be considered that plant metabolome or proteome is in some way a manifestation of its phenotype, but I think that in a stricter sense, we should employ the term "phenotype" in regard of the visual appearence of organs, tuissues or cells of plants.

Whereas the lab and greenhouse conditions could have ideal condictions to study subtler effects (and one-by-one), at the end the most valuable application will be on the field.

I think phenotyping ("phenomics"?) is of outstanding interest since at the end, a lot of our efforts to improve genetic, proteomic or metabolomic traits are reflected in the plant´s external aspect (yield, biomass, pathogen resistance, height...), and a correct and strict quantification of them is essential.

I am starting to employ some phenotyping tools in order to study stress effects on Arabidopsis plants.

From my side, it should be in field.