﴿حَافِظُوا عَلَى الصَّلَوَاتِ وَالصَّلَاةِ الْوُسْطَى﴾
Maintain the prayers, and especially the middle prayer. (Al-Baqarah 2:238)
The plural al-ṣalawāt already includes the middle prayer. Mentioning al-ṣalāt al-wusṭā separately calls special attention to it; the conjunction does not remove it from the class of prayers.
Grammatically, al-wusṭā qualifies al-ṣalāh. The separately coordinated phrase remains within the scope of the general injunction but receives additional emphasis.