Sitobolium Desv.

Triana-Moreno, Luz A., Yañez, Agustina, Kuo, Li-Yaung, Rothfels, Carl J., Pena, Nelson Túlio L., Schwartsburd, Pedro B. & Sundue, Michael, 2023, Phylogenetic revision of Dennstaedtioideae (Dennstaedtiaceae: Polypodiales) with description of Mucura, gen. nov., TAXON 72 (1), pp. 20-46 : 37-38

III. Sitobolium Desv.

in Mém. Soc. Linn. Paris 6: 262. 1827 [ Sitolobium J.Sm. in J. Bot. (Hooker) 3: 418. 1841, orth. var., Litolobium Newman in Phytologist 5: 236. 1854, orth. var.] – Type: Sitobolium punctilobulum (Michx.) Desv. (≡ Nephrodium punctilobulum Michx. ).

= Adectum Link, Fil. Spec.: 42. 1841 – Type: Adectum pilosiusculum (Willd.) Link (≡ Dicksonia pilosiuscula Willd. ).

= Coptidipteris Nakai & Momose in Cytologia, Vol. Fuji Jub. 1: 365. 1937 [ Coptodipteris , orth. var.] – Type: Coptidipteris wilfordii (T.Moore) Nakai & Momose (≡ Microlepia wilfordii T.Moore ).

= Fuziifilix Nakai & Momose in Cytologia, Vol. Fuji Jub. 1: 365. 1937 – Type: Fuziifilix pilosella (Hook.) Nakai & Momose (≡ Davallia pilosella Hook. ).

= Emodiopteris Ching & S.K.Wu in Acta Phytotax. Sin. 16(4): 21. 1978 – Type: Emodiopteris appendiculata (Wall. ex Hook.) Ching & S.K.Wu (≡ Dicksonia appendiculata Wall. ex Hook. ).

Description. – Plants terrestrial or rupestral; rhizomes short to long creeping, generally branched, with catenate hairs; petioles grooved, adaxially sulcate, bearing epipetiolar buds, unarmed; leaves small to moderately sized, generally less than 1 m long, erect, decompound, 2–4-pinnate, usually with catenate hairs and sometimes glandular hairs, without proliferous leaf buds, axes inalate; veins free, with enlarged apices; sori marginal, provided with abaxial and adaxial indusia fused into a cup-shaped involucre; spores trilete, perispore of prominent ridges and verrucae, or tubercles. ( Fig. 7 )

Synopsis. – Sitobolium is a small clade of ca. five species sister to Microlepia . Sitobolium are distinguished by their relatively small leaves that have elongate catenate hairs. These hairs often bear a capitate non-glandular terminal cell. Sitobolium punctilobulum and S. appendiculatum additionally have glandular hairs. Sitobolium wilfordii , however, is glabrous. All Sitobolium have epipetiolar buds, enlarged vein endings, and marginal cup-shaped sori comprised of both abaxial and adaxial indusia. The epipetiolar buds distinguish them from their closest relatives, Microlepia and Mucura , but this character is homoplastic and widespread in the family. Sitobolium appendiculatum and S. wilfordii have previously been treated as Emodiopteris and Coptidipteris respectively. The two are united in having tuberculate perispore morphology ( Fig. 4B ) (vs. the verrucate perispore, with prominent ridges seen in other Sitobolium species), but otherwise lack diagnostic characters to distinguish them as a distinct genus and are therefore included here. The geographical distribution of Sitobolium is the Northern Hemisphere; most species are East Asian— S. punctilobulum is the single North American species. We recovered it as a sister to the East Asian S. zeylanica (as S. scabra ) as did Schwartsburd & al. (2020), who inferred an early Miocene divergence time between the two. This age estimate corresponds well with a major dispersal event from Asia to North America for many plant groups using the Bering land bridge or North Atlantic land bridges ( Lee & al., 2020).

History of use. – Sitobolium was in use by early authors until Moore (1859) subsumed it under his concept of Dennstaedtia ( Tryon & Tryon, 1980) . The original spelling by Desvaux was altered by J. Smith to ‘ Sitolobium ’, but there is no reason to believe that Desvaux’ s spelling was incorrect.

Taxonomic treatments. – The Asian species have been treated (in Dennstaedtia ) by Knapp (2011) and Yan & al. (2013), and by Fraser-Jenkins & al. (2015, 2017), who updated some taxonomy and nomenclature. Sitobolium punctilobulum , the only species in the Western Hemisphere, was monographed by Conard (1908). We include five constituent species of Sitobolium based upon molecular phylogenetic and morphological evidence, and we make necessary combinations for four of them.

Figures

Fig. 7. Characters of Sitobolium. A, Habit; B, Lower leaf surface and marginal sori with cup-shaped indusia; C, Creeping branched rhizome and petioles with epipetiolar buds; D, Grooved adaxial rachis-costa axes without raised wings. — All photos by M. Sundue except B by R.C. Moran.

Fig. 4. Examples of perispore morphology of spores in distal view. A, Verrucae and irregular reticles with prominent ridges covering the corners, Mucura globulifera (Yañez & Márquez 86, LP); B, Tubercles, Sitobolium wilfordii (Unknown coll. s.n., UVMVT192145, VT); C, Verrucae and prominent ridges to the spore sides, Sitobolium hirsutum (Rothfels & al. 5282, VT); D, Network of rodlets, Microlepia speluncae (Rojas 4878, MO); E, Regular reticle, Dennstaedtia glabrata (James & Sundue 1593, VT); F, Prominent ridges, Dennstaedtia distenta (Mickel 4163, LP); G, Verrucae and ridges, Dennstaedtia dissecta (Palacios 1296, LP). — Scale bars = 10 μm.