Echiteae

Barny, Lea A., Tasca, Julia A., Sanchez, Hugo A., Smith, Chelsea R., Koptur, Suzanne, Livshultz, Tatyana & Minbiole, Kevin P. C., 2021, Chemotaxonomic investigation of Apocynaceae for retronecine-type pyrrolizidine alkaloids using HPLC-MS / MS, Phytochemistry (112662) 185, pp. 1-15 : 8-9

2.6. Echiteae , Odontadenieae, Mesechiteae

These three tribes form a well-supported monophyletic clade of predominantly New World genera ( Fishbein et al., 2018), but the boundaries among them have been redrawn several times ( Morales et al., 2017; Sim˜oes et al., 2004). Morales et al. (2017) proposed that presence of PAs is a useful chemotaxonomic character for delimiting Echiteae from Odontadenieae and identified their absence in Pentalinon Voigt as supportive of its transfer to Odontadenieae. We sampled eight of fourteen Echiteae , five of nine Odontadenieae, and three of six Mesechiteae genera. PAs were detected in seven of eight sampled Echiteae genera. Only the sampled Prestonia species ( P. robusta Rusby , P. tomentosa R.Br. ) had no evidence of PAs in the PREC 120 (MCA on) scans ( Table S2), although PAs have been previously reported from P. amabilis J.F.Morales , P. quinquangularis Spreng. [syn. P. acutifolia (Benth. ex Müll.Arg) K.Schum ], and P. portobellensis Woodson ( Burzynski et al., 2015). PAs in Echites and Parsonsia have been previously reported ( Burzynski et al., 2015), but PAs in Bahiella J.F.Morales , Macropharynx (syn. Peltastes ), Temnadenia , Rhodocalyx Müll.Arg. , and Laubertia A.DC. are here reported for the first time, although Brown (1987) had previously suggested their presence in Macropharynx and Temnadenia based on indirect evidence. Exemplars of these genera had molecular ions appearing at consistent retention times in PREC 120, 138, and 156 scans ( Table 2), fragmentation patterns characteristic of the cyclic triesters known from the positive control, Parsonsia alboflavescens ( Table 1 ). Among the 22 species sampled from the other two tribes ( Table S2), only one, Mandevilla boliviensis (J.J.Veitch) Woodson (Mesechiteae) , yielded an ion detectable in the PREC 120 scan, but not in PREC 138 or 156 ( Table 2). We have low confidence in the identification of this compound as a PA, but this result requires further investigation. Overall, this pattern supports Morales et al. (2017) hypothesis of the chemotaxonomic utility of PA presence for circumscription of Echiteae .

PAs are present in all Echiteae genera studied, but presence of detectable PAs varies both among samples of congeneric species and of conspecific individuals ( Table S2, S 3 , Table 2). The diversity of PAs within a sample also varies greatly from 18 candidate compounds in Parsonsia alboflavescens ( Table 1 ) to one in Temnadenia odorifera (Vell.) J.F.Morales ( Table 2). We have evidence that some of this variation is due to plasticity (see Section 2.11), but the role of genetics remains uncertain. Extensive sampling of species and individuals within Echiteae genera will be necessary to determine if there are any species-specific patterns useful for delimiting sub-tribal or infra-generic taxa.