May function as histone H3 lysine demethylase and be involved in regulation of gene expression (By similarity). Regulates flowering time by promoting CONSTANS (CO) and CONSTANS-LIKE genes (e.g. COL2 and COL5) expression via interaction with FBH transcription factors (FBH1, FBH2, FBH3 and FBH4) at their loci to remove H3K9me2 repressive histone marks (PubMed:33604650). Modulates also the expression of several develpmental genes such as MYB30, TFS1, AGL6 and RVE2 (PubMed:33604650). Binds 1 Fe(2+) ion per subunit. Interacts with the FBH transcription factors FBH1, FBH2, FBH3 and FBH4. Expressed in inflorescences, flowers, roots, siliques, leaves and stems, especially in the vasculature (mainly phloem), with highest levels in floral organs (PubMed:18713399). Present at high levels in flowers, shoot apex and young seeds, but observed at low levels in dry seeds, root apex and anthers (PubMed:33604650). Follows a circadian cycle with lower levels in the early morning and highest accumulation in the middle of the day. No visible phenotype (PubMed:28400174). Decreased hypocotyl length (PubMed:33604650). Delayed flowering associated with reduced FLOWERING LOCUS T (FT) and CONSTANS (CO) levels due to increased H3K9me1/2 level at CO locus (PubMed:33604650). Belongs to the JARID1 histone demethylase family.