As nouns the difference between plantlets and seedling
is that plantlets is while seedling is (botany) a young plant grown from seed.
As an adjective seedling is
which is a seedling (see below).
seedling
English
Noun
(
en noun)
(botany) A young plant grown from seed
Any young, especially
# one grown in a nursery for transplanting
# a tree smaller than a sapling.
References
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