Lachanon refers to garden vegetables or herbs — cultivated edible plants other than grain. It appears 4 times in the NT, most famously in Jesus's parable of the mustard seed ('the smallest of all seeds... the largest of garden plants [lachanon],' Matthew 13:32) and in Paul's discussion of vegetarianism in Romans 14.
The mustard seed parable uses lachanon with deliberate irony: the kingdom of God begins as the most insignificant thing imaginable and becomes something unexpected — not a stately cedar (the OT symbol of imperial power) but a common garden herb that provides shelter. This subverts messianic expectations of grandeur. In Romans 14:2, the 'weak' believer 'eats only vegetables [lachanon]' — Paul uses this as a test case for the principle of not judging those with different scruples, establishing the priority of love over dietary correctness. The humble garden vegetable becomes the occasion for one of the NT's most important discussions of conscience, freedom, and community.