The most common and most likely answer to this crossword clue is the 15 letter word PARTHENOGENESIS
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More clues leading to the result PARTHENOGENESIS
- Book on unfinished temple has unusual origin
- Reproduction Stonehenge assembled in capital
- Unusual reproduction in earphones gets distorted
- Way to reproduce endless Greek temple and first book
- Reformed pioneers sang about the virgin birth
- Conception of retro music followed by old rock group
- Quietly distributing another book of the Bible that describes the Virgin Birth
- Unusual reproduction showing fowl in chapter of Old Testament book
- Heating response messed up reproduction without fertilization
- Eighteen parsons excited — is it virgin birth?
Buddy explains!

The straight part
We know that "Unusual reproduction" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unusual reproduction = parthenogenesis.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PARTHENOGENESIS mean?
PARTHENOGENESIS noun- Referring to various aspects of asexual reproduction:
- Figurative uses of the biological senses
- Virgin birth, in reference to the Virgin Mary and Jesus Christ.