List only posts from specific category on category page

Question

I wanted to ask if there is a shorter way then by checking each time if the post is coming from a specific category.

As you can see the categories cover the alphabet, A B C etc and each time I check with a custom loop etc, is there a shorter way to write this or am I on track.

At the moment how I have it set up works.

<?php  if ( is_category( 'a' )  ) { ?> 
<?php $THEresults = array( 'post_type' => 'plants', 'orderby'=> 'title', 'order' => 'ASC', 'category_name' => 'a',);
    $loop = new WP_Query( $THEresults );
?>
<?php while ( $loop->have_posts() ) : $loop->the_post();?>
<?php get_template_part( 'content' ); ?>
<?php endwhile; ?>

<?php wp_reset_postdata(); ?>

 <?php  } elseif ( is_category( 'b' ) ) { ?>
<?php
    $THEresults = array( 'post_type' => 'plants', 'orderby'=> 'title', 'order' => 'ASC', 'category_name' => 'b',);
    $loop = new WP_Query( $THEresults );
?>
<?php while ( $loop->have_posts() ) : $loop->the_post();?>
<?php get_template_part( 'content' ); ?>
<?php endwhile; ?>

<?php wp_reset_postdata(); ?>

EDIT FROM COMMENTS

I have a custom post type ‘plants’ and the posts created are arranged into categories in alphabetical form such as category A, B, C etc. When you click on category A then the above code will only display those posts in category A, for B, C etc. The above works but didn’t know if there was a shorter way to check if the post belongs to category A, B, C etc 

Answer 1

You are complicating everything with a custom query. You should never ever replace the main query with a custom one on the home page or any type of archive page, this breaks page functionalities as you have seen. You should take your time and read this post I have done on this particular issue

You just need the default loop in category.php, nothing else

if ( have_posts() ) {
    while ( have_posts() ) {
    the_post();

        //Your html and template tags

    }
}

EDIT

Just some extra info for interest sake

You don't need all that statements to check the category. You can simply access the queried object and get whatever needed info from there. get_queried_object() returns the complete queried object, get_queried_object_id() returns the current object id. So you could have just passed the following to your query arguments

'cat' => get_queried_object_id(),

instead of doing al those plenty if/else statements

EDIT 2

It seems your biggest headche is actually your custom post type. By default, they are excluded from the main query on category pages. With the changes you've made according to recommendation from my original past, you will not see custom post type posts, just posts from the default post type post

As I have described in the linked post, you should use pre_get_posts to alter the main query to suite your needs. And this what you should do here as well.

In your functions.php, you need to add the following code, this will add your custom post type to your category pages

add_action( 'pre_get_posts', function ( $q ) 
{
    if ( !is_admin() && $q->is_main_query() && $q->is_category() ) {
        $q->set( 'post_type', array( 'post', 'plants' ) ); //This will show normal posts and plants
    }
});

The above will now show normal posts and posts from the post type plants. If you don't need to show normal posts, just remove post from the array