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Boron nitride (BN) layers with sp(2) bonding have been grown by metal organic chemical vapor deposition on AlN underlayers, which are deposited on c-plane sapphire substrates. Two different boron precursors were employed-trimethylboron and triethylboron-while ammonia was used as the nitrogen precursor. The BN obtained epitaxial BN films contain ordered rhombohedral (rBN) and partially ordered turbostratic (tBN) stackings as evidenced by x-ray diffraction analysis. We discriminatively identify the PL signatures of the rBN and tBN from those typical of the hexagonal (hBN) and Bernal stackings (bBN). The optical signature of tBN appears at 5.45eV, and it intercalates between the two recombination bands typical of rBN at 5.35eV (strong intensity) and 5.55eV(weaker intensity). The analogs of the high intensity band at 5.35eV in rBN sit at 5.47eV for hBN and at 5.54eV for bBN. ; Funding Agencies|network GaNeX [ANR-11-LABX-424 0014]; BONASPES project [ANR-19-CE30 0007]; ZEOLIGHT project [ANR-19-CE08-0016]; Universite de Montpellier; Swedish Research CouncilSwedish Research CouncilEuropean Commission [2017-04164]; Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [IS14-0027]; Carl Tryggers Foundation for Scientific Research [CTS 14:189]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoping University [2009-00971]; Office of Naval ResearchOffice of Naval Research [N00014-20-1-2474, 428]; National Science FoundationNational Science Foundation (NSF) [CMMI 429, 1538127]

G.Á.-P. and J.T.-G. acknowledge support through the Severo Ochoa Program from the Government of the Principality of Asturias (nos. PA-20-PF-BP19-053 and PA-18-PFBP17-126, respectively). J.M.-S. acknowledges financial support through the Ramón y Cajal Program from the Government of Spain (RYC2018-026196-I). A.Y.N. and J.I.M. acknowledge the Spanish Ministry of Science, Innovation and Universities (national projects MAT201788358-C3- 3-R and PID2019-104604RB/AEI/10.13039/501100011033). R.H. acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities (national project RTI2018-094830-B-100 and the project MDM-2016-0618 of the Marie de Maeztu Units of Excellence Program) and the Basque Government (grant No. IT1164-19). A.Y. N. also acknowledges the Basque Department of Education (grant no. PIBA-2020-1- 0014). P.A.-G. acknowledges support from the European Research Council under starting grant no. 715496, 2DNANOPTICA and the Spanish Ministry of Science and Innovation (State Plan for Scientific and Technical Research and Innovation grant number PID2019-111156GB-I00).