Oldest indications

Alternatives on Bosscher:
Cristianus Buschera, 1221;
Waltero Buskere, Meulebeke 1230;
Maes de Busschere, Izegem 1382;
Adriaens de Busschere of Adriaens de Buyschere, 1400;
Bossin de Bosschere, 1409;
Bussart de Bosschere, Kortrijk 1414;
Oste Bussaert de Bosschere, Kortrijk 1427.

Compare the names Bosschaert and Bossaert, etc.. and Van den Bossche
Jan van den Bussche zegge (called) Buschaert, 1410 is the same person as Jan Busschaerts; Jhan Bosscart, Kortrijk 1418
Jhan van den Bussche ... van Busscharde vorseit, 1410
Jhan van den Bussche slouch ... Hanekin Notebart seit dat Busschart slouch, Kortrijk 1410

Bossaert, etc. is a patronym of Bouchard and derived from Burghard.
Bouchart le Ferpier of Burchard 1300;
Gheraerd Bortsaerd, Assenede 1322;
Coppin Bossaerd, brood, Ieper 1373; of Jacob Bossaerd, Coppin Bossard 1374; Jacob Bossard etc. Jacop Bossaerd 1380
Jan Bossaerd, wever, Ieper 1378;
Michiel Bossaerd, Ieper 1378; of Mich(iel) Bossaert 1395; of Mich(iel) Bossard 1398;
Bossaerd Bonte ... Bussaert vorseit Dottenijs 1382;
Jan Bossaerd, Wervik 1382;
Cateline Bossaerts, vlees, Ieper 1392;
Bossaerd de Bosschere 1409 (is dezelfde persoon als Bossin de Bosschere 1409);
Oste Bussaert de bosschere, Kortrijk 1427.

Boshart, Bosshart as an equivalent of Bossaert, Burchard:
Heinrich Boshart, Hamburg 1306.

Bosschert
Andries Bosschert, captive of the Imposition in 1585 of Amsterdam; is the same person as Andries Bosschaert, of Antwerp, 33 years, who married in Amsterdam in 1594.