Root tuberization patterns in Commelinaceae: a new anatomical approach

Abstract Tuberous roots in monocots exhibit considerable variation in shape and size, yet their development and anatomical diversity remain poorly understood in Commelinaceae. This study investigates the morphological and anatomical diversity of tuberous roots in seven species representing three of the four major lineages in the family— Palisota , Commelineae, and Tradescantieae s.s.—with emphasis on the tuberization patterns. Tuberous root samples from Palisota barteri , Commelina platyphylla , Dichorisandra leucophthalma , D. marantoides , D. radicalis , D. thyrsiflora , and Tradescantia pallida were collected and fixed in FAA50 and embedded in both Historesin and Paraplast. We carried out morphometric analyses, as root diameter, cortical cells number (CCN), vascular parenchyma cell number (VPCN), and phloem area (PA), from transverse sections of tuberous roots, and we revealed two distinct morphological types of tuberous roots: the stalked shaped characterized by having two non-thickened extremities and a thickened median region and the sessile shaped, with thickening uniform along all the root. In general, the dermal system and cortical region on the thickened region of both stalked and sessile shaped roots, do not differ from what was observed in the non-thickened region. However, in the vascular system our results show four anatomical patterns: (1) In the first pattern the parenchyma of the centre of the vascular cylinder in the non-thickened region is not lignified, whereas, in the thickened region, it is composed of lignified cells; (2) In the second pattern, all parenchyma cells of the centre of the vascular cylinder are lignified, both in the non-thickened and in the thickened region; (3) In the third pattern the parenchyma of the centre of the vascular cylinder is composed of non-lignified cells in both regions (thickened and non-thickened); and (4) The last pattern reveals a fragmentation of the vascular system observed only in Dichorisandra , and the parenchyma of the centre of the vascular cylinder in the non-thickened region is lignified, whereas, in the thickened region, it is composed of expanded storage parenchyma. In the cortical region, a protective tissue was observed only in Tradescantia pallida , from subepidermal or outer cortical cells. Bifurcated root hairs were observed in Commelina platyphylla , P. barteri and T. pallida . With the new contributions to the understanding of the structural processes involved in root tuberization in Commelinaceae, we encourage studies using this approach in other Commelinoideae, and especially in other subfamilies as Cartonematoideae.