Thesidium (Sonder, 1857)

García, Miguel A., Mucina, Ladislav & Nickrent, Daniel L., 2024, A tough nutlet to crack: Resolving the phylogeny of Thesium (Thesiaceae), the largest genus in Santalales, TAXON 73 (1), pp. 190-236 : 200-202

5. Thesidium clade:

Thesium subg. Hagnothesium (BIPP 1). — To maintain a monophyletic Thesium ( Forest & Manning, 2013) , species previously classified in the genus Thesidium ( Sonder, 1857) were reclassified as Thesium sect. Hagnothesium A.DC. Zhigila & al. (2020). They later raised this section to the rank of subgenus (T. subg. Hagnothesium (A.DC.) Zhigila & al.). These species are CFR endemics and include annual to shrubby plants with mostly tetramerous flowers and a dioecious sexual condition. Some species, including T. microcarpum A.DC, T. fragile ( Fig. 3C ) and T. quartzicolum Zhigila & al. have morphologically similar male and female plants (monomorphic) whereas T. fruticulosum (A.W.Hill) J.C.Manning & F.Forest, T. minus (A.W.Hill) J.C.Manning & F.Forest, T. strigulosum A.DC. (= T. hirtum (Sond.) Zhigila & al., nom. illeg.), T. longicaule Zhigila & al. and T. leptostachyum A.DC. are dimorphic. In the latter case, male plants usually have small herbaceous bracts and female plants have conspicuous leafy bracts. Although we only sampled five species, the ITS phylogeny ( Fig. 2A ) resolves two highly supported clades separating sexually dimorphic and monomorphic species.

The nuclear and chloroplast phylogenies suggest that Thesium subg. Hagnothesium is an early-divergent lineage that, in spite of being endemic to the CFR, is more closely related to Eurasian, North African, and Canary Islands lineages (T. subg. Thesium ). According to our chloroplast phylogeny it is sister to T. subg. Thesium , however this relationship is not resolved by ITS. Instead, T. subg. Hagnothesium is nested within T. subg. Thesium (clade 2), making the latter paraphyletic.

Unsampled species include T. leptostachyum , T. longicaule , T. quartzicolum , and T. strigulosum .

Figures

Fig. 3. Caption on next page.

Fig. 2. Phylogenetic analysis of Thesium using nuclear ribosomal internal transcribed spacer (ITS) sequences. This tree, rooted with Osyridicarpos and Lacomucinaea (outgroups) gives Bayesian posterior probabilities at the nodes. Clades discussed in the text are numbered. Geographical sources for the sampled taxa are abbreviated as follows: AFN = Northern Africa, AFS = Southern Africa, AFT = Tropical Africa, ASC = Central Asia, ASE = Eastern Asia, ASN = Northern Asia, ASS = Southern Asia, ASW = Western Asia, AUS = Australia, CIS = Canary Islands, EUR = Europe, MAD = Madagascar, SAM = South America, and USA = United States of America.