Why should we reverentially pluck flowers or leaves for puja?

However divine may be the purpose,
flowers and leaves are integral parts of the
plants. By plucking them, the plants are hurt.
Thus by mentally or orally asking their
permission, a devoted person tries to understand the presence of divine life in all.
Mantras such as –

maa nu shOkam, kurushva tvam
sthaanatyaagam cha maa kuru |
dEvataapoojanaarthaaya
praarthayaami vanaspatE ||

are addressed to the plants before
plucking flowers or leaves. One should also
not pluck flowers or leaves after sunset.