Vivipary is defined as the precocious and continuous growth of the offspring when still attached to the maternal parent; in the case of plants, it would pertain by definition to the continual growth of the embryo, essentially germination before it ought to occur. Mangroves are viviparous. Ordinarily, plant embryos undergo a period of quiescence, the genes which code for molecular cascades that govern embryo dormancy and subsequent release to growth are still not well known. and perhaps I don't want to know all of their little quaint molecules anyways.
In FNA Vol. 26 vivipary is attributed to blue-eye grass (Sisyrinchium) with the statement "White flowers may occur in otherwise blue-flowered species, and vivipary occasionally occurs". My observation of Sisyrinchium bellum suggests that the purported yivipary is not vivipary per se, but is rather considered pseudovivipary.
In Sisyrinchium bellum, the inflorescence nodes develop subsidiary vegetative axes which initiate and develop well after flowering; resulting in vegetative reproduction. The inflorescence axis in large, perennial races of S. bellum arch downwards, and the nodes are often in contact with the soil, resulting in vegetative expansion, but hardly is this vivipary in the strict sense. This feature is variable in nature, and rarely have I seen it in grassland settings. However, Sisyrinchium bellum is also a weed-of-sorts in forested-setting gardens like mine in the Santa Cruz Mountains of California.
The pseudo-vivipary feature can be clearly seen it the photo of the voucher specimen, JEPS109033.