Maidenhair Spleeenwort – Asplenium trichomanes

PNA or Pna has a variety of meanings:

Science and engineering

abbreviation for orchid genus Paphinia
Pacific–North American teleconnection pattern, a climatic phenomenon
Parisiensia Nomina Anatomica, the revision of anatomic nomenclature
Peanut agglutinin, a lectin specific for Gal-β(1–3)-GalNAc
Peptide nucleic acid, an artificially synthesized polymer similar to DNA or RNA.
Plastic neutral axis, an engineering value used in plastic section modulus
Pottery Neolithic A, a division of the Pottery Neolithic period in archaeology

Pakistan National Alliance
Palestinian National Authority, an administrative autonomous government in parts of the West Bank and the Gaza Strip
Partido Nacional Agrarista (National Agrarian Party), a Mexican left-wing agrarian political party founded in 1920
Partidul Național-Agrar (National Agrarian Party), a Romanian right-wing agrarian political party active in the 1930s
Project for Nuclear Awareness, a non-profit organization that advocates for the abolition of nuclear weapons, co-founded by John C. Haas
Polish National Alliance, a non-profit organization, the largest Polish – American Fraternal Benefit Society in USA offering life insurance and annuities. Founded in 1880, operates solely for the benefit of its members.
Pa-O National Army
Partido Nueva Alianza, the Spanish name for the New Alliance Party (Mexico)
Parties to the Nauru Agreement
Pennsylvania NewsMedia Association
Philippine Nurses Association
Prefectura Naval Argentina, the Spanish name for the Argentine Naval Prefecture
National Anticorruption Directorate, Romania; formerly, National Anticorruption Prosecution Office (PNA)