plural noun
Pen·​na·​les | \pəˈnā(ˌ)lēz\

Definition of Pennales 

: an order of diatoms having a raphe or pseudoraphe and ornamentation of the valves always bilaterally arranged in relation to a line rather than to a point — compare centrales

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History and Etymology for Pennales

New Latin, from Latin penna feather + New Latin -ales

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having a pattern of small flowers

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