The second section of subgenus Panzhihuaensis, section Indosinensis Schuster, 1932 (in Engler, Pflanzenr. 99: 65; subgenus Pectinata de Laub., 1998, Blumea 43: 375, based on C. pectinata), is distinguished by the fruits having a fibrous layer, by the seeds not having a verrucose surface, by the 5-15 mm rigid sterile apical part of the microsporophyll more or less erect and blunt to triangular with a sharply deflected  apical spine , and by the midvein of the pinnae prominent on both sides.  The pinnae are flat or the margins slightly bent.  Lateral segments on the apex of the megasporophyll are 18-25 mm or a little longer and 2-3 or sometimes 4 mm at the base, diminishing in size slightly towards the apical spine which projects prominently and generally bears a few reduced lateral segments.  The yellow to orange fruits are not pruinose.  Distributed from eastern India across all of southeastern Asia and over the border a bit into China and in the Philippines.  There are seven species and the type is C. siamensis. 

Cycas siamensis Miquel, 1863 (Bot. Zeit. 21: 334) 
C. immersa Craig, 1912 (Kew Bull. 1912: 434) 
C. nongnoochiae Hill, 1999 (Brittonia 51: 60) 
C. pachypoda Hill, 2004 (Bot. Rev. 70: 176) 
Distinguished by the huge subterranean bulb eventually giving way to a robust trunk to several meters high.  The flat leaves are up to 130 cm long or a little more and about one sixth thorny petiole.  The spinescent tipped pinnae are 6-18 cm x 4-9 mm and diminish basally in size to thorns.  The pollen cones are barrel-shaped and up to 30 x 10 cm.  The apical spine on the microsporophyll is 5-15 mm long.  The lateral segments on the megasporophyll are up to 20 mm long with an apical spine to 45 mm long.  The fruits are up to 37 x 37 mm.  The corky bark becomes split  and checkered due to environmental stress.  The grey-green leaves of C. nongnoochiae with longer petioles and larger pinnae (to 23 cm x 12 mm) suggest introgression with C. clivocola and could be considered a variety.  The grey-green leaves of C. pachypoda whose pinnae reduce only weakly basally with pollen cones up to 49 x 15 cm also suggest some kind of introgression.  Distributed from the borders of Burma across most of Thailand and into Viet Nam.  A specimen from Bhutan is probably from a cultivated specimen.   

Cycas pectinata Buch,-Ham., 1825 (Mem. Wern. Soc. 5: 322) 
Distinguished by huge ovoid acute pollen cones to 69 x 22 cm whose microsporophylls have apical spines up to 40 mm long.  The smooth trunk has a greatly swollen base and can reach to 15 meters high with branches.  The flat grey-green leaves are up to 240 cm long and about one fifth mostly thorny petiole.  The pinnae are up to 32 cm x 6-10 mm.  The segments of the megasporophyll are up to 25 mm long with an apical spine up to 75 mm long.  The fruits are up to 45 x 45 mm.  Distributed  from eastern India across northern Burma and western Thailand and just across the border into China. 

Cycas macrocarpa Griff., 1854 (Not. Pl. As. 4: 11) 
Distinguished by the large fruits to 53 x 45 mm and by the not spinescent tipped pinnae 18-45 cm x 12-20 mm.  The trunk may be lightly fissured and up to l2 meters high, but no more than slightly enlarged at the base.  The flat green leaves may reach 320 cm long about a quarter of which is mostly thorny petiole.  The pinnae gradually reduce basally in size to thorns.  The ovoid pollen cones reach 35 x 12 cm.  The apical spine of the microsporophyll is up to 28 mm long.  The segments on the megasporophyll are up to 18 mm long with an apical spine to 60 mm. Endemic to Penninsular Thailand and nearby parts of Penninsular Malaysia. 

Cycas riuminiana Porte, 1863 (in Regel, Gartenfl. 12: 16) 
C. chamberlainii Br. & Kienholz, 1925 (Philipp. Jour. Sci. 26: 47) 
Distinguished by the spinescent tipped pinnae 16-32 cm x 7-11 mm and by the ovoid pollen cones to 32 x 8 cm. The sturdy trunk up to 8 meters tall is not swollen at the base.  The flat green leaves are up to 230 cm long and about one quarter mostly thorny petiole.  The ovoid pollen cones apparently reach to about 32 x 16 cm.  The apical spine on the microsporophyll is up to 11 mm long.  The segments on the megasporophyll are up to 18 mm long with an apical spine up to 57 mm long.  The fruits are up to 50 x  36 mm.  Restricted to two small areas on Luzon. 

Cycas elongata (Leandri) Yang, 1996 (in Wang & Liang, Cycads in China: 51; C. pectinata Buch.-Ham. Var elongata Leandri, 1931 in Lecompt & Gagn., Fl. Gen Indo-chine 5: 1091) 
C tansachana Hill & Yang, 1999 (Brittonia 51: 65) 
C. condaoensis Hill & Yang, 2004 (Bot. Rev. 70: 178) 
C. petrea Lindstrom & Hill, 2002 (Brittonia 54: 299) 
C. currani (Schust.) Hill, 1995 (Proc. Third Int. Conf. Cycad Biol.: 150; C. circinalis 
L subsp. riuminiana Porte var curanni Schust., 1932 in Engler, Pflanzenr. 99: 69) 
C. changjiangensis Liu, 1998 (Acta Phytotax. Sin. 36: 552) 
Distinguished by barrel-shaped slightly tapering pollen cones to 45 x 13 cm or even larger, by megasporophyll segments to 25 mm with an apical spine to 60 mm or even longer, and by not spinescent tipped pinnae 13-30 cm x 7-13 mm.  Trunks corky and often becoming cracked and checkered, with a greatly enlarged base which starts out as a bulb.  Slightly keeled leaves to 180 cm or longer with about one quarter petiole usually provided with some thorns.  Apical spine on the microsporophyll to 8 mm or more.  Fruit to 50 x 40 mm.  Distributed across the southern parts of Thailand to Viet Nam and Hainan Island.  Populations in particularly stressed environments (tansachana and condaoensis) have the checkered bark.  C. petrea, in central Thailand, has longer segments on the megasporophyll (to 40 mm), fatter pollen cones (to 18 cm), and flat leaves, as well as longer (to 20 mm) apical spines on the microsporophyll.  These are not strong differences but could well be the basis for a variety.  The case of C. curanni is puzzling.  It involves a small population on Palawan Island directly across the South China Sea from the widely distributed C. elongata and is a perfect match except for the report of grooved seeds.  It has been poorly known but, because it occurs in the Philippines and has pectinate apices of the megasporophyll, it has been likened to C. wadei which has grooved seeds.  I suspect that somehow this character became erroneously attached to C. currani.  Apparently C. elongata widely overlaps the distribution of C. clivicola which it resembles.  For example, Tang et al (1997, Cycads of Thailand: 14) under C. clivicola illustrates a tree with keeled leaves and checkered bark with a barrel-shaped pollen cone, the leaves having the typical ragged look of C. elongata, in the southernmost part of Thailand.  But Tang also (2001, Encephalartos 67: 12) illustrates a typical C. clivicola pollen cone from the same area.  Likewise, both kinds of pollen cone have been illustrated for southern Viet Nam where C. elongata originates (see under C. clivicola). 

Cycas clivicola Hill, 1999 (Brittonia 51: 62) 
C. chamaoensis Hill, 1999 (Brittonia 51: 58) 
C. elephantipes Lindstrom & Hill, 2002 (Brittonia 54: 301) 
C. inermis Lour., 1790 (Fl. Cochin. 1: 632), illeg., given in synonomy with C revoluta Thunb. 
Distinguished by the ovoid-lanceolate pollen cones to 63 x 16 cm and by the flat grey-green leaves to 250 cm long with spinescent tipped pinnae 9-30 cm x 7-11 mm.  The stem is corky, becoming checkered in severe environments, and enlarged at the base.  The petiole is about one quarter of the leaf and usually has some thorns.  The apical spine on the microsporophyll reaches 14 mm long.  The lateral segments on the megasporophyll reach 40 mm long and the apical spine to 75 mm long.  The fruits are up to 40 x 35 mm.  Distributed across southernmost Thailand and Viet Nam and into Penninsular Malaysia.  C. elephantipes from central Thailand has checkered bark, longer segment on the megasporophyll (55 mm), and a longer spine on the microsporophyll (30 mm).  Vietnamese botanists have identified examples of C. clivicola as C. pectinata because of the similar looking pollen cones, tapering to an acute apex, but these are noticeably more slender than those of C. pectinata.  Vorstar illustrates this pollen cone from cultivation in Viet Nam (identified, however, as C. elongata, 2002, Encephalartos 72: 20, and Osborne et al, 2007, Cycads of Viet Nam: 84).  That both C. clivicola and C. elongata occur in this part of Viet Nam is indicated by the report of Osborne et al (79) that pinnae here are “spinescent or not spinescent” and by the remark of T. Walters to me that he found some megasporophylls in this area to be elongated (that would be elongata) and others more like C. siamensis (that would be clivcola).  Miquel (1851, Analecta Bot. Indica II: 40-46, plates III-IV) extensively described C. clivicola from cultivated material he got from Bogor identified as C. inermis from China.  Surely Bogor had inermis from Lourero himself and shortened Cochinchina, from where inermis originated, to “China.”  Smitinand (l971, Nat. Hist. Bull. Siam Soc. 24: 170; 1972, Flora of Thailand: 187), under C. pectinata, clearly illustrated a C. clivicola pollen cone (he included C. clivicola collections under his C. pectinata; see also under C. elongata).

Cycas lindstromii Yang & Hill, 1997 (Novon 7: 213) 
Distinguished by a subterranean branched bulb with no aerial growth whatsoever, by slightly keeled leaves to 100 cm long and one quarter of which is thorny petiole, and by not spinescent tipped pinnae which are 10-17 cm x 77-11 mm.  Pollen cones barrel-shaped and 16-29 x 4-5 cm.  The apical spine on the microsporophyll reaches 8 mm long.  Segments on the apical part of the megasporophyll reach at least 15 mm and the apical spine up to 50 mm long.  The fruit reaches 37 x 33 mm.  Endemic to a small area in southern Viet Nam.