Solanum echinatum
n = ploidy missing =12 voucher: Symon 5155 (ADW) (Randell & Symon 1976)
Solanum echinatum is common in the Northern Territory and is found in the northwestern corner of Queensland, Australia. In Queensland it occurs as far south as Mt. Isa, and in the Northern Territory it also occurs on the islands of the Gulf of Carpentaria. It also occurs in the Kimberley region of Western Australia. It grows on stony ridges or gullies in low eucalypt woodland, on a variety of substrates, including laterite.
Solanum echinatum is a typical member of Solanum subgenus Leptostemonum. It is placed into the S. echinatum group (Group 27F) by Bean (2004) on morphological grounds; its phylogenetic position has not been investigated using molecular data.
Randell, B.R. & D.E. Symon 1976. Chromosome numbers in Australian Solanum species.
Aust. J. Bot. 24: 369-379.
Symon, D.E. 1981. A revision of Solanum in Australia.
J. Adelaide Bot. Gard. 4: 1-367.
Bean, A.R. 2004. The taxonomy and ecology of Solanum subg. Leptostemonum (Dunal) Bitter (Solanaceae) in Queensland and far north-eastern New South Wales.
Austrobaileya 6 (4): 639-816.
Solanum echinatum is closely related to S. longissimum, but differing by the sparsely prickly branchlets with 3-80 prickles per dm (vs. 200-660 for S. echinatum); branchlet prickles 6-10 times longer than wide (10-20 times for S. echinatum); the dense stellate hairs on the branchlets (vs. very dense for S. echinatum); the very long petioles, 65-115% of lamina length (vs. 25-55% for S. echinatum); and the deltate calyx lobes 1-2.5 mm long (vs. rostrate to attenuate, 3-6 mm long for S. echinatum).
Both S. echinatum and S. longissimum have numerous conspicuously stalked stellae, especially on the branchlets and rachis, but also to a lesser degree on the upper and lower leaf surfaces. The calyx prickles are extremely numerous, and there are always some smaller prickles with stellae mounted at the top (or, from the other perspective, long-stipitate stellae which are becoming prickles). By contrast, the stellae of S. senticosum (which grows in the same area) have stalks all about the same length with none conspicuously long. Also, none of the calyx prickles of S. senticosum have stellae mounted at the top. Hence S. echinatum and S. longissimum can be readily separated from S. senticosum in the absence of fruiting material.
Symon (1981) counted (41-) 107 (-185) seeds per fruit in 14 fruits from three collections of S. echinatum and (192-) 254 (-330) seeds per fruit in 8 fruits of what he recognised as S. seitheae. Symon (1981) also noted that the plants of S. echinatum are usually rusty-pubescent or less frequently greyish; some very small leaved plants have also been collected and it is rarely clear whether this is a seasonal effect or reflects other causes. Prickles on the calyx vary in density and there is some evidence that cleistogamous forms occur. The fruits are finally shed when mature and plants collected in the dry season are often without fruits, especially if they are small. The prickly calyx and easily shed ripe fruit enable them to function as “trample burrs” and this is a probable means of distribution. The fruits of S. lucani are not so readily shed.
The type of S. seitheae is indistinguishable from the type of S. echinatum. They both have fruits of about the same size, a dense rusty tomentum, some leaves with shallow lobes, and petioles less than half as long as the lamina. Symon (1981) originally distinguished S. seitheae from S. echinatum on the basis of its larger size, subshrubby habit, generally grey pubescence, and larger flowers and fruits.
There are additional unnamed taxa related to S. echinatum in the Northern Territory, and S. wilkinsii is possibly distinct enough to warrant recognition at the species level.
Conservation status: Widespread. Not considered at risk.