Some are particular to purchase a Lulav with the brownish leaf covering called the Kara. Others are particular not to purchase such a Lulav. [The Rebbe was particular to purchase a Lulav which its top leaves are attached with a brownish leaf called a Kara. ]
 Oatzer p. 271; See “Halachos of Four Species” Chapter 11 in Hebrew section; p. 97; Piskeiy Teshuvos 645/3
 The reason: In order to suspect for the opinion of the Geonim that the Tiyomes must be closed in with the other leaves and not loose.
 Oatzer p. 271; See “Halachos of Four Species” Chapter 11 in Hebrew section.