Complex sentence: Hybridization with the Japanese rose ("Rosa rugosa") has been recorded in eastern North America, the concern being the invasive potential of vigorous F1 hybrids and genetic assimilation of the native species.
Split into simpler sentences: Hybridization with the Japanese rose ("Rosa rugosa") has been recorded in eastern North America. This is a cause for concern over the potential for development of vigorous hybrids with invasive potential and genetic assimilation of the native species.