Developmental Morphology of the Controversial Ramulus Organ ofTristicha trifaria(Subfamily Tristichoideae, Podostemaceae): Implications for Evolution of a Unique Body Plan in Podostemaceae

Developmental morphology of flattened shoots in Dalzellia ubonensis and Indodalzellia gracilis with implications for the evolution of diversified shoot morphologies in the subfamily Tristichoideae (Podostemaceae)

“…For the three genera, phyllotaxis similarly begins from the tristichous, although the shape of the shoot apex and orientation of marginal leaves differ. The shoot apex of Indodalzellia and Dalzellia is flatter than that of Tristicha , and the marginal leaves are arranged almost vertically in Indodalzellia and Dalzellia but horizontally in Tristicha (designated as ventral leaves for Tristicha ; Fujinami et al, 2013) (Fig. 7B, D, G).…”

“…The evolution of adaptive morphology is one of the most important topics of research in the field of botany. Podostemaceae, which are aquatic angiosperms that grow on rock surfaces in rapids and waterfalls of the tropics and subtropics, show unparalleled unique morphologies that have fascinated researchers since the beginning of the 20th century (e.g., Willis, 1902a, b, 1914, 1915; Engler, 1930; Troll, 1937; Jäger‐Zürn, 1970; Cook, 1990; Rutishauser, 1997; Koi et al, 2006; Cook and Rutishauser, 2007; Katayama et al, 2010; Fujinami et al, 2013). The plant bodies of the Podostemaceae are submerged and continuously subject to swift‐running water during the rainy season.…”

“…Therefore, these shoot‐like organs were once considered an enigmatic organ called the ramulus (Willis, 1902a, b; Rutishauser and Huber, 1991). However, recent studies of the comparative development of the plant bodies of Terniopsis and Tristicha clarified that the ramulus is the determinate shoot produced as the result of sympodial branching (Jäger‐Zürn, 1997; Fujinami and Imaichi, 2009; Fujinami et al, 2013). In contrast, the foliose shoot of Dalzellia apparently lacks ramulus‐like elongated shootlets (Fig.…”

“…In the current study, we examined the comparative development of shoots of I. gracilis and D. ubonensis , focusing on the arrangement of leaves (phyllotaxis) and sites of branching to compare their development with that shoots of Terniopsis and Tristicha of Tristichoideae, which have leaves arranged in tristichous phyllotaxis and lateral branches that arise as extra‐axillary buds of leaves (Fujinami and Imaichi, 2009; Fujinami et al, 2013). For I. gracilis , we first observed shoots that had just arisen on the flank of a creeping root.…”

Historical biogeography of river-weeds (Podostemaceae)

“…(1) Shoot organogenesis (character code 1 in Table 3) Tristichoideae (Dalzellia, Indodalzella, Indotristicha, Terniopsis, Tristicha) have typical shoot apical meristems (SAMs) on the periphery of which the leaves are produced acropetally and adaxial-abaxial to the stem (Rutishauser and Huber, 1991;Jäger-Zürn, 1997a;Imaichi et al, 1999Imaichi et al, , 2004Koi et al, 2009;Fujinami and Imaichi, 2009;Koi and Kato, 2010a;Fujinami et al, 2013). Weddellinoideae have also SAMs producing dorsiventral leaves acropetally, but additional leaves are produced basipetally from an intercalary meristem (Koi and Kato, 2007).…”